Documentation/replace: state that objects must be of the same type

A previous patch ensures that both the replaced and the replacement
objects passed to git replace must be of the same type, except if
-f option is used.

While at it state that there is no other restriction on both objects.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-replace.txt

@@ -20,8 +20,13 @@ The name of the 'replace' reference is the SHA-1 of the object that is
 replaced. The content of the 'replace' reference is the SHA-1 of the
 replacement object.
 
+The replaced object and the replacement object must be of the same type.
+This restriction can be bypassed using `-f`.
+
 Unless `-f` is given, the 'replace' reference must not yet exist.
 
+There is no other restriction on the replaced and replacement objects.
+
 Replacement references will be used by default by all Git commands
 except those doing reachability traversal (prune, pack transfer and
 fsck).
@@ -69,9 +74,7 @@ go back to a replaced commit will move the branch to the replacement
 commit instead of the replaced commit.
 
 There may be other problems when using 'git rev-list' related to
-pending objects. And of course things may break if an object of one
+pending objects.
-type is replaced by an object of another type (for example a blob
-replaced by a commit).
 
 SEE ALSO
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