Re #6581 Backport documentation improvements

Author: mpilgrem

doc/global_flags.md

@@ -345,7 +345,7 @@ Default: `https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots
 The `--snapshot-location-base <url>` command option specifies the base location
 of snapshots.
 
-## `--help` command flag
+## `--help` or `-h` command flags
 
-If Stack is passed the `--help` command flag, it will output help for the
-command.
+If Stack is passed the `--help` (or `-h`) command flag, it will output help for
+the command.

doc/other_resources.md

@@ -6,8 +6,8 @@ There are lots of resources available for learning more about Stack:
 
 * `stack` or `stack --help` — lists Stack's commands, and flags and options
   common to those commands
-* `stack <command> --help` — provides help on the particular Stack command,
-  including flags and options specific to the command
+* `stack <command> --help` (or `-h`) — provides help on the particular Stack
+  command, including flags and options specific to the command
 * `stack --version` — identify the version and Git hash of the Stack executable
 * `--verbose` (or `-v`) — much more info about internal operations (useful for
   bug reports)