Merge pull request #1038 from notlmn/grammar

add omitted word

book/07-git-tools/sections/submodules.asc

@@ -384,7 +384,7 @@ This means that there is no local working branch (like ``master'', for example)
 With no working branch tracking changes, that means even if you commit changes to the submodule, those changes will quite possibly be lost the next time you run `git submodule update`.
 You have to do some extra steps if you want changes in a submodule to be tracked.
 
-In order to set up your submodule to be easier to go in and hack on, you need do two things.
+In order to set up your submodule to be easier to go in and hack on, you need to do two things.
 You need to go into each submodule and check out a branch to work on.
 Then you need to tell Git what to do if you have made changes and then `git submodule update --remote` pulls in new work from upstream.
 The options are that you can merge them into your local work, or you can try to rebase your local work on top of the new changes.