update contribution guide

CONTRIBUTING.md

@@ -0,0 +1,22 @@
+# Want to contribute?
+
+Microsoft's documentation for VS Code extensions is suprisingly good (https://code.visualstudio.com/docs/extensions/overview);
+
+## Workspace preparation
+Fortunately VSCode has js/ts support out of the box.
+
+1. install VS Code, `npm`, `nodejs`
+1. clone project
+1. disable auto carriage return `git config core.autocrlf false; git reset --hard`
+1. open VS Code, select project's folder, open terminal and type `npm install` (this will download dependencies)
+1. Run by clicking **Ctrl+F5**, new VS window will open
+
+# Build CI
+
+Using Travis CI (https://travis-ci.org/rogalmic/vscode-bash-debug)
+
+- Every push to master will create a release in github with `vsix` package for testing
+- Every tag pushed to master matching `v1.2.3` will trigger a deploy to VSCode extension repo with this version.
+  - Remember to use [proper commit messages](https://github.com/conventional-changelog/standard-version#commit-message-convention-at-a-glance).
+  - Keep version in project.json same as version in git tag, best to achieve by running `npm run release -- --release-as minor` to bump version and create commit with [proper tag](https://docs.npmjs.com/cli/version#git-tag-version) at the same time.
+  - Push the tag `git push origin v1.2.3`, this will start the publish build in [TravisCI](https://travis-ci.org/rogalmic/vscode-xml-complete).