doc: branch guidelines

CONTRIBUTING.md

@@ -4,6 +4,12 @@ When contributing to this repository, please first discuss the change you wish t
 
 Join the telegram channel: https://t.me/StarknetByExample
 
+The release branch is `main`. The development branch is `dev` and is considered stable (but not released yet).
+When you want to contribute, please create a new branch from `dev` and open a pull request to merge your changes back into `dev`.
+You should never open a pull request to merge your changes directly into `main`.
+
+The `dev` branch is deployed at https://starknet-by-example-dev.voyager.online/
+
 Please note we have a code of conduct, please follow it in all your interactions with the project.
 
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