Update CONTRIBUTING.md
Update CONTRIBUTING.md

--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -1,23 +1,24 @@
-## Contributing
+# Contributing
 Changes and improvements are more than welcome! Feel free to fork and open a pull request.
 
 Please follow the house rules to have a bigger chance of your contribution being merged.
 
-### House rules
+## House rules
 
-#### How to make changes
+### How to make changes
  - To make changes, create a new branch based on `master` (do not create one from `gh-pages` unless strictly necessary) and make them there, then create a Pull Request to master.  
  `gh-pages` is different from master in that it contains sharing features, analytics and other things that have no direct bearing with the game. `master` is the "pure" version of the game.
  - If you want to modify the CSS, please edit the SCSS files present in `style/`: `main.scss` and others. Don't edit the `main.css`, because it's supposed to be generated.  
- In order to compile your SCSS modifications, you need to use the `sass` gem (install it by running `gem install sass` once Ruby is installed). To run SASS, simply use the following command:  
+ In order to compile your SCSS modifications, you need to use the `sass` gem (install it by running `gem install sass` once Ruby is installed).  
+ To run SASS, simply use the following command:  
  `sass --watch style/main.scss`  
  SASS will automatically recompile your css when changed.
  - `Rakefile` contains some tasks that help during development. Feel free to add useful tasks if needed.
  - Please use 2-space indentation when editing the JavaScript. A `.jshintrc` file is present, which will help your code to follow the guidelines if you install and run `jshint`.
  - Please test your modification thouroughly before submitting your Pull Request.
 
-#### Changes that might not be accepted
-We have to be conservative in regards to the core game. This means that some modifications won't be merged, or will have to be evaluated carefully before doing being merged:
+### Changes that might not be accepted
+We have to be conservative with the core game. This means that some modifications won't be merged, or will have to be evaluated carefully before being merged:
 
  - Undo/redo features
  - Save/reload features
@@ -25,7 +26,7 @@
  - Changes to the layout
  - Changes to the grid size
 
-#### Changes that are welcome
+### Changes that are welcome
  - Bug fixes
  - Compatibility improvements
  - "Under the hood" enhancements

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