Document git-grep and link it from the main git(7) page.

Also adjust missing description in the git.txt page while we are at it.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

.gitignore

@@ -31,6 +31,7 @@ git-fetch-pack
 git-format-patch
 git-fsck-objects
 git-get-tar-commit-id
+git-grep
 git-hash-object
 git-http-fetch
 git-init-db

Documentation/git-grep.txt

+git-grep(1)
+===========
+v0.99.6, Sep 2005
+
+NAME
+----
+git-grep - print lines matching a pattern
+
+
+SYNOPSIS
+--------
+'git-grep' <option>... <pattern> <path>...
+
+DESCRIPTION
+-----------
+Searches list of files `git-ls-files` produces for lines
+containing a match to the given pattern.
+
+
+OPTIONS
+-------
+<option>...::
+	Either an option to pass to `grep` or `git-ls-files`.
+	Some `grep` options, such as `-C` and `-m`, that take
+	parameters are known to `git-grep`.
+
+<pattern>::
+	The pattern to look for.
+
+<path>...::
+
+	Optional paths to limit the set of files to be searched;
+	passed to `git-ls-files`.
+
+
+Author
+------
+Written by Linus Torvalds <torvalds@osdl.org>
+
+Documentation
+--------------
+Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
+
+GIT
+---
+Part of the link:git.html[git] suite
+

Documentation/git.txt

 git(7)
 ======
-v0.99.5, Aug 2005
+v0.99.6, Sep 2005
 
 NAME
 ----
@@ -238,7 +238,7 @@ link:git-commit.html[git-commit]::
 	Previously this command was known as git-commit-script.
 
 link:git-diff.html[git-diff]::
-	git-diff.
+	Show changes between commits, commit and working tree, etc.
 	Previously this command was known as git-diff-script.
 
 link:git-fetch.html[git-fetch]::
@@ -246,9 +246,12 @@ link:git-fetch.html[git-fetch]::
 	Previously this command was known as git-fetch-script.
 
 link:git-format-patch.html[git-format-patch]::
-	git-format-patch.
+	Prepare patches for e-mail submission.
 	Previously this command was known as git-format-patch-script.
 
+link:git-grep.html[git-grep]::
+	Print lines matching a pattern
+
 link:git-log.html[git-log]::
 	Shows commit logs.
 	Previously this command was known as git-log-script.