doc: improve language in contribute

Previous wording was incorrect.

Change-Id: I91406c775161d9724ec60824c156e8e9a925bcd7
GitHub-Last-Rev: 2b6b4e136a78a431cc847a2717cbeae4341ed7bc
GitHub-Pull-Request: golang/go#28248
Reviewed-on: https://go-review.googlesource.com/c/142879Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

doc/contribute.html

@@ -393,8 +393,8 @@ Remember you can always visit Gerrit to see the fine-grained review.
 <p>
 It is not possible to fully sync Gerrit and GitHub, at least at the moment,
 so we recommend learning Gerrit.
-It's different but powerful and familiarity
-with help you understand the flow.
+It's different but powerful and familiarity with it will help you understand
+the flow.
 </p>
 
 <h3>Overview</h3>