[git] reflect branch rename from 'master' to 'main' (#6249)

CONTRIBUTING.md

@@ -63,7 +63,7 @@ For each new feature, create a working branch:
 
 ```bash
 # Create a working branch for your new feature
-git branch --track <branch-name> origin/master
+git branch --track <branch-name> origin/main
 
 # Checkout the branch
 git checkout <branch-name>
@@ -85,16 +85,16 @@ This will open up a text editor where you can craft your commit message.
 
 Prior to submitting your pull request, you might want to do a few things to clean up your branch and make it as simple as possible for the original repo's maintainer to test, accept, and merge your work.
 
-If any commits have been made to the upstream master branch, you should rebase your development branch so that merging it will be a simple fast-forward that won't require any conflict resolution work.
+If any commits have been made to the upstream main branch, you should rebase your development branch so that merging it will be a simple fast-forward that won't require any conflict resolution work.
 
 ```bash
-# Fetch upstream master and merge with your repo's master branch
-git checkout master
-git pull upstream master
+# Fetch upstream main and merge with your repo's main branch
+git checkout main
+git pull upstream main
 
 # If there were any new commits, rebase your development branch
 git checkout <branch-name>
-git rebase master
+git rebase main
 ```
 
 Now, it may be desirable to squash some of your smaller commits down into a small number of larger more cohesive commits. You can do this with an interactive rebase:
@@ -102,7 +102,7 @@ Now, it may be desirable to squash some of your smaller commits down into a smal
 ```bash
 # Rebase all commits on your development branch
 git checkout
-git rebase -i master
+git rebase -i main
 ```
 
 This will open up a text editor where you can specify which commits to squash.