Add git-checkout example for files across branches

pages/common/git-checkout.md

@@ -2,14 +2,18 @@
 
 > Checkout a branch or paths to the working tree.
 
-- Switch to another branch:
-
-`git checkout {{branch_name}}`
-
 - Create and switch to a new branch:
 
 `git checkout -b {{branch_name}}`
 
+- Switch to an existing branch:
+
+`git checkout {{branch_name}}`
+
 - Undo unstaged local modification:
 
 `git checkout .`
+
+- Replace a file in the current working directory with the version of it committed in a given branch:
+
+`git checkout {{branch_name}} -- {{file_name}}`