git-delete-submodule: add page (#8553)

pages/common/git-delete-submodule.md

@@ -0,0 +1,9 @@
+# git delete-submodule
+
+> Delete a specific submodule from a `git` repository.
+> Part of `git-extras`.
+> More information: <https://github.com/tj/git-extras/blob/master/Commands.md#git-delete-submodule>.
+
+- Delete a specific submodule:
+
+`git delete-submodule {{path/to/submodule}}`