Documentation/clone: document ignored configuration variables

Due to limitations in the current implementation, some configuration
variables specified via 'git clone -c var=val' (or 'git -c var=val
clone') are ignored during the initial fetch and checkout.

Let the users know which configuration variables are known to be
ignored ('remote.origin.mirror' and 'remote.origin.tagOpt') under the
documentation of 'git clone -c', along with hints to use the options
'--mirror' and '--no-tags' instead.

Signed-off-by: SZEDER Gábor <[email protected]>
Reviewed-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: szeder

Documentation/git-clone.txt

@@ -189,6 +189,12 @@ objects from the source repository into a pack in the cloned repository.
 	values are given for the same key, each value will be written to
 	the config file. This makes it safe, for example, to add
 	additional fetch refspecs to the origin remote.
++
+Due to limitations of the current implementation, some configuration
+variables do not take effect until after the initial fetch and checkout.
+Configuration variables known to not take effect are:
+`remote.<name>.mirror` and `remote.<name>.tagOpt`.  Use the
+corresponding `--mirror` and `--no-tags` options instead.
 
 --depth <depth>::
 	Create a 'shallow' clone with a history truncated to the