Improve the contribution guide

Author: Calinou

CONTRIBUTING.md

@@ -1,11 +1,10 @@
-#How to contribute
+# How to contribute
 
-If you want to contribute you can follow these setps:
-- Fist create your own clone of assimp
-- When you want to fix a bug or add a new feature create a branch on your own fork ( just follow https://help.github.com/articles/creating-a-pull-request-from-a-fork/ )
-- Push it to the repo and open a pull request
-- A pull request will start our CI-service, which checks if the build works for linux and windows. 
-  It will check for memory leaks, compiler warnings and memory alignment issues. If any of these tests fails: fix it and the tests will be reastarted automatically
-  - At the end we will perform a code review and merge your branch to the master branch.
-  
-  
+If you want to contribute, follow these steps:
+
+- First, create your own clone of assimp.
+- When you want to fix a bug or add a new feature, create a branch on your own fork following [these instructions](https://help.github.com/articles/creating-a-pull-request-from-a-fork/).
+- Push it to your fork of the repository and open a pull request.
+- A pull request will start our continuous integration service, which checks if the build works for Linux and Windows.
+  It will check for memory leaks, compiler warnings and memory alignment issues. If any of these tests fail, fix it and the tests will be restarted automatically.
+  - At the end, we will perform a code review and merge your branch to the master branch.