[llvm-ar][nfc] Reword help message to be less ambiguous on what p and t do.

[oontvoo]

Summary

The current help msg isn't super clear on whether t prints the content of the files or just the list of files.
(I'd certainly thought it'd print the list of files, and accidentally had a bunch of "gargabe" printed to my terminal).
Similarly, t sounded like it'd do what p actually did.

[MaskRay]

LGTM.

llvm/tools/llvm-ar/llvm-ar.cpp

--rsp-quoting         - quoting style for response files
     =posix              -   posix
     =windows            -   windows
   --version             - print the version and exit
   @<file>               - read options from <file>
 
 OPERATIONS:
   d - delete [files] from the archive
   m - move [files] in the archive
-  p - print [files] found in the archive
+  p - print contents of [files] found in the archive
   q - quick append [files] to the archive
   r - replace or insert [files] into the archive
   s - act as ranlib
-  t - display contents of archive
+  t - display list of files in archive
   x - extract [files] from the archive
 
 MODIFIERS:
   [a] - put [files] after [relpos]
   [b] - put [files] before [relpos] (same as [i])
   [c] - do not warn if archive had to be created
   [D] - use zero for timestamps and uids/gids (default)
   [h] - display this help and exit