added branch sync line

Author: mthalman

Documentation/Renovate.md

@@ -60,6 +60,7 @@ This means that Renovate acts as though it's any other outside contributor, not
 A GitHub bot account, `dotnet-renovate-bot`, is used to manage the Renovate operations.
 This account has the ability to create forks from dotnet repositories, which will be the source of the head branch for PRs that are created.
 The PRs generated by Renovate will be done using this bot account.
+Renovate also handles synchronization from the upstream branch automatically.
 GitHub scopes required by this account: `repo`, `workflow`.
 
 ### Repo Usage