Documentation: update add and submodule describing the ignore=all and --force

Signed-off-by: Claus Schneider(Eficode) <claus.schneider@eficode.com>

Author: bicschneider

Documentation/git-add.adoc

@@ -77,7 +77,9 @@ in linkgit:gitglossary[7].
 
 `-f`::
 `--force`::
-	Allow adding otherwise ignored files.
+	Allow adding otherwise ignored files. The option is also used
+	when updating submodules and `submodule.<name>.ignore=all`
+	is set. The `path` to the submodule must be explicitly specified.
 
 `--sparse`::
 	Allow updating index entries outside of the sparse-checkout cone.

Documentation/gitmodules.adoc

@@ -70,7 +70,10 @@ submodule.<name>.ignore::
 --
 	all;; The submodule will never be considered modified (but will
 	    nonetheless show up in the output of status and commit when it has
-	    been staged).
+	    been staged). Add `(new commits)` can be overruled using the
+		`git add --force <submodule.path>` similar to ignored files. The setting has effect
+		for `status`, `update-index`, `diff` and `log`(due to underlaying
+		 `diff`)
 
 	dirty;; All changes to the submodule's work tree will be ignored, only
 	    committed differences between the `HEAD` of the submodule and its