Added instruction to delete contents when overwriting main line - #11726

[vale] reported by reviewdog 🐶 [Mendix.Capitalization] Use ''Git'' (capitalized) Raw Output: {"message": "[Mendix.Capitalization] Use ''Git'' (capitalized)", "location": {"path": "content/en/docs/refguide/version-control/using-version-control-in-studio-pro/managing-branches.md", "range": {"start": {"line": 89, "column": 105}}}, "severity": "ERROR"}