Update README.md to include branch matching information (#373)

Signed-off-by: Pip Potter <[email protected]>
Co-authored-by: Mike Balfour <[email protected]>
Co-authored-by: allisaurus <[email protected]>

README.md

@@ -117,6 +117,16 @@ These instructions use the following installation paths. Be sure to substitute y
    echo o3de-multiplayersample-assets > C:/o3de/.git/info/exclude
    ```
 
+## Step 1a. Ensure your branches match
+
+Before building the project, ensure that o3de, o3de-multiplayersample and o3de-multiplayersample-assets are all cloned from the same named branches. For example, if you are using the **development** branch of o3de-multiplayersample, then it must be matched with the **development** branches of o3de, and o3de-multiplayersample-assets. Ensure that you update the submodules in o3de-multiplayersample-assets when switching branches in that repository.
+
+If you're using a release or installer version of O3DE, then you must checkout versions of the sample repositories that match the release. O3DE uses standard Git [tags](https://git-scm.com/book/en/v2/Git-Basics-Tagging) to identify the release-compatible version of each repository. 
+
+For each O3DE release, repositories that have been updated to match the release should have a matching tag for the release. You can see all defined tags using the [Tags](https://github.com/o3de/o3de-multiplayersample/tags] view in each repository.
+
+Branches can be checked out using standard Git commands, for example, `git checkout tags/<tag> -b <local branch name>`.
+
 ## Step 2. Register the engine, the project, and the Gems
 
 ### Option #1 - Use the CLI