Create check_out_remote_branch.md

git/check_out_remote_branch.md

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+# Checking out someone else's branch 
+
+## Use case 
+
+A colleague has opened a PR. I want to check out their branch on my own machine so I can run it and test their changes 
+
+## Instructions 
+
+- Get the branch name that you want
+- Back in your terminal, run `git fetch` to load all the remote branch
+- Then run `git checkout <branch-name>`
+
+Another "thing I have known for a while but sometimes forget."