Fix language.

Author: samcunliffe

slides.md

@@ -493,9 +493,9 @@ Rank each of these bug reports...
 ---
 
 1. Clone to your computer.
-2. (Optional) Create a branch and switch to it.
+2. Create a branch and switch to it.
 3. Add yourself [like this](https://github.com/CCMI-CDT/ccmi-cdt.org/pull/53/files).
-4. Commit changes and push to your fork.
+4. Commit changes and push to your branch.
 5. Open a pull request.
 6. Review someone else's PR.
 7. Squash merge!