fix: Updates setup instructions to add .gitkeep (#56)

running `git add -A` without any files to stage results in nothing to commit so the branch is never created.

README.md

@@ -33,7 +33,7 @@ git add -A && git commit -m "Added ember-cli-github-pages addon"
 Then you need to create the `gh-pages` branch and remove the unnecessary files:
 
 ```sh
-git checkout --orphan gh-pages && rm -rf `bash -c "ls -a | grep -vE '\.gitignore|\.git|node_modules|bower_components|(^[.]{1,2}/?$)'"` && git add -A && git commit -m "initial gh-pages commit"
+git checkout --orphan gh-pages && rm -rf `bash -c "ls -a | grep -vE '\.gitignore|\.git|node_modules|bower_components|(^[.]{1,2}/?$)'"` && touch .gitkeep && git add -A && git commit -m "initial gh-pages commit"
 ```
 
 ## Usage