Update to reflect beta package support and document prerequisites

ReadMe.md

@@ -1,11 +1,11 @@
 # <img src="https://cdn.jsdelivr.net/gh/brogers5/chocolatey-package-messenger@11eade7e5c9cf02a523fc1a90c744a146ba806b7/messenger.png" width="48" height="48"/> Chocolatey Package: [Messenger](https://community.chocolatey.org/packages/messenger)
 
-[![Chocolatey package version](https://img.shields.io/chocolatey/v/messenger.svg)](https://community.chocolatey.org/packages/messenger)
-[![Chocolatey package download count](https://img.shields.io/chocolatey/dt/messenger.svg)](https://community.chocolatey.org/packages/messenger)
+[![Total package download count shield](https://img.shields.io/chocolatey/v/messenger.svg?include_prereleases)](https://community.chocolatey.org/packages/messenger)
+[![Total package download count shield](https://img.shields.io/chocolatey/dt/messenger.svg)](https://community.chocolatey.org/packages/messenger)
 
 ## Install
 
-[Install Chocolatey](https://chocolatey.org/install), and run the following command to install the latest approved version from the Chocolatey Community Repository:
+[Install Chocolatey](https://chocolatey.org/install), and run the following command to install the latest approved stable version from the Chocolatey Community Repository:
 
 ```shell
 choco install messenger --source="'https://community.chocolatey.org/api/v2'"
@@ -17,6 +17,8 @@ Alternatively, the packages as published on the Chocolatey Community Repository
 choco install messenger --source="'.;https://community.chocolatey.org/api/v2/'"
 ```
 
+This package also supports the project's beta builds. Opt into these with the `--prerelease` switch.
+
 ## Build
 
 [Install Chocolatey](https://chocolatey.org/install), clone this repository, and run the following command in the cloned repository:
@@ -33,6 +35,8 @@ Note that Chocolatey package builds are non-deterministic. Consequently, an inde
 
 This package should be automatically updated by the [Chocolatey Automatic Package Updater Module](https://github.com/majkinetor/au). If it is outdated by more than a few days, please [open an issue](https://github.com/brogers5/chocolatey-package-messenger/issues).
 
+### AU Setup
+
 AU expects the parent directory that contains this repository to share a name with the Nuspec (`messenger`). Your local repository should therefore be cloned accordingly:
 
 ```shell
@@ -45,6 +49,36 @@ Alternatively, a junction point can be created that points to the local reposito
 mklink /J messenger ..\chocolatey-package-messenger
 ```
 
-Once created, simply run `update.ps1` from within the created directory/junction point. Assuming all goes well, all relevant files should change to reflect the latest version available. This will also build a new package version using the modified files.
+### Beta Stream Setup
+
+The update script will request the latest version information for both the stable and beta channels directly from Messenger's Sparkle service.
+
+While information for the stable channel may be anonymously queried, the beta channel requires access to a Facebook account that has joined Messenger's beta testing program. Users can opt into this directly in Messenger - from the menu bar, browse to **File** > **Preferences** > **General**, and toggle **Join beta testing**:
+
+![Screenshot of beta testing toggle](https://cdn.jsdelivr.net/gh/brogers5/chocolatey-package-messenger@5010723f82c0b6b79779417af1bb1bee15001cc0/BetaTestingToggle.png)
+
+Requests for beta version information will also require sending authentication cookies that contain the account's static user ID ([`c_user`](https://cookiedatabase.org/cookie/facebook/c_user/)) and a dynamic unique session ID ([`xs`](https://cookiedatabase.org/cookie/facebook/xs/)). We can take advantage of session riding to reuse an existing session ID from PowerShell and minimize authenticating to Facebook.
+
+The script depends on [PowerShell's `SecretManagement` module](https://devblogs.microsoft.com/powershell/secretmanagement-and-secretstore-are-generally-available/) to securely query for the cookies' values from a registered extension vault.
+
+If you do not already have an extension vault registered, install [an extension vault module](https://www.powershellgallery.com/packages?q=Tags%3A%22SecretManagement%22) of your choice, then [register a secret vault](https://learn.microsoft.com/powershell/module/microsoft.powershell.secretmanagement/register-secretvault?view=ps-modules) as required by the module's implementation.
+
+Log into Facebook from your web browser, [grab the cookies' values](https://www.cookieyes.com/blog/how-to-check-cookies-on-your-website-manually/), then create the following secrets:
+
+```powershell
+#TODO: Populate using values sourced from web browser
+$c_userValue = ''
+$xsValue = ''
+
+Set-Secret -Name 'Facebook User ID' -Secret $c_userValue
+Set-Secret -Name 'Facebook Session ID' -Secret $xsValue
+```
+
+>**Note**
+>The session ID secret will require occasional updates to work around sessions expiring or otherwise being invalidated by Facebook (e.g. logging out, password changes, device removal, suspicious account activity, etc.).
+
+### Execution and Testing
+
+Once everything is set up, simply run `update.ps1` from within the created directory/junction point. Assuming all goes well, all relevant files should change to reflect the latest version available. This will also build a new package version using the modified files.
 
 Before submitting a pull request, please [test the package](https://docs.chocolatey.org/en-us/community-repository/moderation/package-verifier#steps-for-each-package) with a 64-bit Windows 10 v1903+ environment similar to the [Chocolatey Testing Environment](https://github.com/chocolatey-community/chocolatey-test-environment) first.