docs: Add JS vars documentation (#63)

Signed-off-by: Leonardo Luz Almeida <leonardo_almeida@intuit.com>

README.md

@@ -85,6 +85,15 @@ spec:
             value: https://github.com/argoproj-labs/argocd-ephemeral-access/releases/download/v0.1.0/extension.tar.gz
           - name: EXTENSION_CHECKSUM_URL
             value: https://github.com/argoproj-labs/argocd-ephemeral-access/releases/download/v0.1.0/extension_checksums.txt
+          - name: EXTENSION_JS_VARS
+            value: |
+              {
+                "EPHEMERAL_ACCESS_LABEL_KEY": "some-label/is-production",
+                "EPHEMERAL_ACCESS_LABEL_VALUE": "true",
+                "EPHEMERAL_ACCESS_MAIN_BANNER": "All production changes require an associated change request. Click the REQUEST ACCESS button above to automatically create a change request associated with your user",
+                "EPHEMERAL_ACCESS_MAIN_BANNER_ADDITIONAL_INFO_LINK": "https://link-to-some-documentation.com",
+                "EPHEMERAL_ACCESS_DEFAULT_ROLE": "devops"
+              }
           volumeMounts:
             - name: extensions
               mountPath: /tmp/extensions/
@@ -101,6 +110,22 @@ spec:
           emptyDir: {}
 ```
 
+> [!NOTE]
+> The `EXTENSION_JS_VARS` is an special variable. It contains the UI
+> extension configurations. If provided, the
+> `argocd-extension-installer` will automatically create the js file
+> to expose the provided values to the UI extension. The following
+> table describes the js variables accepted by the EphemeralAccess UI
+> extension:
+
+| Name                                                | Description                                                                                       | Required | Default |
+| --------------------------------------------------- | ------------------------------------------------------------------------------------------------- | -------- | ------- |
+| `EPHEMERAL_ACCESS_DEFAULT_ROLE`                     | Defines the RoleName to be associated with users once the AccessRequest is created                | Yes      | -       |
+| `EPHEMERAL_ACCESS_LABEL_KEY`                        | If provided, it will only enable the UI extension if the Argo CD Application has this label key   | No       | -       |
+| `EPHEMERAL_ACCESS_LABEL_VALUE`                      | If provided, it will only enable the UI extension if the Argo CD Application has this label value | No       | -       |
+| `EPHEMERAL_ACCESS_MAIN_BANNER`                      | A text with the brief description to instruct users about how the extension works                 | No       | -       |
+| `EPHEMERAL_ACCESS_MAIN_BANNER_ADDITIONAL_INFO_LINK` | An additional link to provide users with more detailed documentation                              | No       | -       |
+
 ### Enabling the EphemeralAccess extension in Argo CD
 
 Argo CD needs to have the proxy extension feature enabled for the