Documentation/git-rm: correct submodule description

Since 3ccd681c2a (Merge branch 'sb/submodule-rm-absorb', 2017-01-18)
git-rm tries to absorb any submodules git dir before deleting the
submodule. Correct the documentation to say so.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-rm.txt

@@ -140,10 +140,11 @@ Only submodules using a gitfile (which means they were cloned
 with a Git version 1.7.8 or newer) will be removed from the work
 tree, as their repository lives inside the .git directory of the
 superproject. If a submodule (or one of those nested inside it)
-still uses a .git directory, `git rm` will fail - no matter if forced
-or not - to protect the submodule's history. If it exists the
-submodule.<name> section in the linkgit:gitmodules[5] file will also
-be removed and that file will be staged (unless --cached or -n are used).
+still uses a .git directory, `git rm` will move the submodules
+git directory into the superprojects git directory to protect
+the submodule's history. If it exists the submodule.<name> section
+in the linkgit:gitmodules[5] file will also be removed and that file
+will be staged (unless --cached or -n are used).
 
 A submodule is considered up-to-date when the HEAD is the same as
 recorded in the index, no tracked files are modified and no untracked