config.txt: Add gitcvs.db* variables

Adds documentation for gitcvs.{dbname,dbdriver,dbuser,dbpass}
Texts are mostly taken from git-cvsserver.txt whith some
adaptions so that they make more sense out of the context
of the original man page.

Signed-off-by: Frank Lichtenheld <frank@lichtenheld.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/config.txt

@@ -408,6 +408,33 @@ gitcvs.logfile::
 	Path to a log file where the cvs pserver interface well... logs
 	various stuff. See gitlink:git-cvsserver[1].
 
+gitcvs.dbname::
+	Database used by git-cvsserver to cache revision information
+	derived from the git repository. The exact meaning depends on the
+	used database driver, for SQLite (which is the default driver) this
+	is a filename. Supports variable substitution (see
+	gitlink:git-cvsserver[1] for details). May not contain semicolons (`;`).
+	Default: '%Ggitcvs.%m.sqlite'
+
+gitcvs.dbdriver::
+	Used Perl DBI driver. You can specify any available driver
+        for this here, but it might not work. git-cvsserver is tested
+	with 'DBD::SQLite', reported to work with 'DBD::Pg', and
+	reported *not* to work with 'DBD::mysql'. Experimental feature.
+	May not contain double colons (`:`). Default: 'SQLite'.
+	See gitlink:git-cvsserver[1].
+
+gitcvs.dbuser, gitcvs.dbpass::
+	Database user and password. Only useful if setting 'gitcvs.dbdriver',
+	since SQLite has no concept of database users and/or passwords.
+	'gitcvs.dbuser' supports variable substitution (see
+	gitlink:git-cvsserver[1] for details).
+
+All gitcvs variables except for 'gitcvs.allbinary' can also specifed
+as 'gitcvs.<access_method>.<varname>' (where 'access_method' is one
+of "ext" and "pserver") to make them apply only for the given access
+method.
+
 http.sslVerify::
 	Whether to verify the SSL certificate when fetching or pushing
 	over HTTPS. Can be overridden by the 'GIT_SSL_NO_VERIFY' environment