Use <> brackets to indicate mandatory parameter

Square brackets [] indicate an optional parameter. In
`git checkout -- <file>` the filename is mandatory.

Author: crd

book/02-git-basics/sections/undoing.asc

@@ -121,7 +121,7 @@ You can see that the changes have been reverted.
 
 [IMPORTANT]
 =====
-It's important to understand that `git checkout -- [file]` is a dangerous command.
+It's important to understand that `git checkout -- <file>` is a dangerous command.
 Any changes you made to that file are gone – you just copied another file over it.
 Don't ever use this command unless you absolutely know that you don't want the file.
 =====