[Git:change] Add a command to show a file as it appeared at <commit id>.

cheatsheets/git

@@ -38,6 +38,7 @@ git checkout master                                     # Checkout local master
 git checkout -b new_branch                              # Create and checkout a new branch
 git merge upstream/master                               # Merge remote into local repo
 git show 83fb499                                        # Show what a commit did.
+git show 83fb499:path/fo/file.ext                       # Shows the file as it appeared at 83fb499.
 git diff branch_1 branch_2                              # Check difference between branches
 git log                                                 # Show all the commits
 git status                                              # Show the changes from last commit