add docs

Signed-off-by: Faeka Ansari <[email protected]>

docs/docs/35-references/10-promotion-steps.md

@@ -539,6 +539,53 @@ steps:
 |------|------|-------------|
 | `commitMessage` | `string` | A description of the change(s) applied by this step. Typically, a subsequent [`git-commit`](#git-commit) step will reference this output and aggregate this commit message fragment with other like it to build a comprehensive commit message that describes all changes. |
 
+### `json-update`
+
+`json-update` updates the values of specified keys in any JSON file.
+
+#### `json-update` Configuration
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| `path` | `string` | Y | Path to a JSON file. This path is relative to the temporary workspace that Kargo provisions for use by the promotion process. |                      |
+| `updates` | `[]object` | Y | The details of changes to be applied to the file. At least one must be specified. |
+| `updates[].key` | `string` | Y | The key to update within the file. For nested values, use a JSON dot notation path. See [sjson documentation](https://github.com/tidwall/sjson) for supported syntax. |
+| `updates[].value`| `any` | Y | The new value for the key. Typically specified using an expression. Supports strings, numbers, booleans, arrays, and objects. |
+
+#### `json-update` Example
+
+```yaml
+vars:
+- name: gitRepo
+  value: https://github.com/example/repo.git
+steps:
+- uses: git-clone
+  config:
+    repoURL: ${{ vars.gitRepo }}
+    checkout:
+    - commit: ${{ commitFrom(vars.gitRepo).ID }}
+      path: ./src
+    - branch: stage/${{ ctx.stage }}
+      create: true
+      path: ./out
+    - uses: git-clear
+      config:
+        path: ./out
+- uses: json-update
+  config:
+    path: configs/settings.json
+    updates:
+    - key: image.tag
+      value: ${{ imageFrom("my/image").Tag }}
+# Render manifests to ./out, commit, push, etc...
+```
+
+#### `json-update` Output
+
+| Name | Type | Description |
+|------|------|-------------|
+| `commitMessage` | `string` | A description of the change(s) applied by this step. Typically, a subsequent [`git-commit`](#git-commit) step will reference this output and aggregate this commit message fragment with other like it to build a comprehensive commit message that describes all changes. |
+
 ### `yaml-update`
 
 `yaml-update` updates the values of specified keys in any YAML file. This step