Merge pull request #10230 from gtirloni/devel

Add how to load extra variables directly from a file (using @).

docs/man/man1/ansible-playbook.1.asciidoc.in

@@ -54,7 +54,8 @@ environment variable.
 *-e* 'VARS', *--extra-vars=*'VARS'::
 
 Extra variables to inject into a playbook, in key=value key=value format or
-as quoted JSON (hashes and arrays).
+as quoted JSON (hashes and arrays). To load variables from a file, specify
+the file preceded by @ (e.g. @vars.yml).
 
 *-f* 'NUM', *--forks=*'NUM'::