add documentation for installing pre-release versions on the marketplace (#1467)

Author: matthewbastien

CONTRIBUTING.md

@@ -32,7 +32,7 @@ When you first open the project in VS Code you will be recommended to also insta
 
 To run your version of the Swift extension while in VS Code, press `F5`. This will open up another instance of VS Code with it running. You can use the original version of VS Code to debug it.
 
-### Installing a pre-released version
+### Installing Pre-Release Builds
 
 If you'd like to try out a change during your day to day work that has not yet been released to the VS Code Marketplace you can build and install your own `.vsix` package from this repository.
 
@@ -54,6 +54,18 @@ Alternatively you can install the extension from the Extensions panel by clickin
 
 If you'd like to return to using the released version of the extension you can uninstall then reinstall Swift for VS Code from the Extensions panel.
 
+#### Pre-Release Builds on the Marketplace
+
+Occasionally, pre-release builds will be published to the VS Code Marketplace. You can switch to the pre-release version by clicking on the `Switch to Pre-Release Version` button in the Extensions View:
+
+![](docs/images/install-pre-release.png)
+
+Switching back to the release version can be done by clicking on the `Switch to Release Version` button.
+
+Release builds for the extension will always have an even minor version number (e.g. `2.0.2`). Pre-release versions will always be one minor version above the latest release version with a patch version set to the day that the VSIX was built (e.g. `2.1.20250327`). These rules are enforced by CI.
+
+The version number in the [package.json](package.json) should always match the most recently published build on the VS Code Marketplace.
+
 ## Submitting a bug or issue
 
 Please ensure to include the following in your bug report: