Update documentation to include information on breaking change docs

Author: cormacpayne

CONTRIBUTING.md

@@ -104,6 +104,12 @@ If splitting up the pull request is not an option, we recommend **creating indiv
 
 For more information on cleaning up the commits in a pull request, such as how to rebase, squash, and cherry-pick, click [here](./documentation/cleaning-up-commits.md).
 
+#### Breaking Changes
+
+Breaking changes should **not** be introduced into the repository without giving customers at least six months notice. For a full list of breaking changes in Azure PowerShell, click [here](https://github.com/Azure/azure-powershell/blob/dev/documentation/breaking-changes.md).
+
+Whenever a service team announces a breaking change, they must add it to the `upcoming-breaking-changes.md` file in their respective service folder. When the service team is ready to release the module with the breaking change, they must move the corresponding information from `upcoming-breaking-changes.md` into the `current-breaking-changes.md` file located in their service folder.
+
 #### General guidelines
 
 The following guidelines must be followed in **EVERY** pull request that is opened.