Documentation: point git-prune users to git-gc

Most users should be using git-gc instead of directly
calling prune. For those who really do want more information
on pruning, let's point them at git-fsck, which goes into
slightly more detail on reachability.

And since we're pointing users there, let's make sure
reflogs are mentioned in git-fsck(1).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-fsck.txt

@@ -22,7 +22,8 @@ OPTIONS
 	An object to treat as the head of an unreachability trace.
 +
 If no objects are given, git-fsck defaults to using the
-index file and all SHA1 references in .git/refs/* as heads.
+index file, all SHA1 references in .git/refs/*, and all reflogs (unless
+--no-reflogs is given) as heads.
 
 --unreachable::
 	Print out objects that exist but that aren't readable from any

Documentation/git-prune.txt

@@ -13,6 +13,9 @@ SYNOPSIS
 DESCRIPTION
 -----------
 
+NOTE: In most cases, users should run linkgit:git-gc[1], which calls
+git-prune. See the section "NOTES", below.
+
 This runs `git-fsck --unreachable` using all the refs
 available in `$GIT_DIR/refs`, optionally with additional set of
 objects specified on the command line, and prunes all
@@ -50,6 +53,23 @@ borrows from your repository via its
 $ git prune $(cd ../another && $(git-rev-parse --all))
 ------------
 
+Notes
+-----
+
+In most cases, users will not need to call git-prune directly, but
+should instead call linkgit:git-gc[1], which handles pruning along with
+many other housekeeping tasks.
+
+For a description of which objects are considered for pruning, see
+git-fsck's --unreachable option.
+
+See Also
+--------
+
+linkgit:git-fsck[1],
+linkgit:git-gc[1],
+linkgit:git-reflog[1]
+
 Author
 ------
 Written by Linus Torvalds <torvalds@osdl.org>