Improve contribution guidelines

Author: michidk

CONTRIBUTING.md

@@ -2,31 +2,31 @@
 
 Let's help together and make a great list of free Unity scripts!
 
-If you know a resource which is not listed here, make a pull request or open an issue. But please read this file first.
-Please report broken links, outdated assets and spelling mistakes.
+If you know a resource that is not listed here, please start a pull request adding your resource after reading this document.
+Please report broken links, outdated assets, and spelling mistakes.
 
 ## Notes:
 * The links are in no particular order.
-* Outdated assets are removed from time to time.
-* GitHub-links are preffered over other hosting locations (like the Unity AssetStore)
+* Outdated assets are removed from time to time (please report outdated assets in issues).
+* Links to open source repository services like GitHub or GitLab are preferred over other providers (like the Unity Asset Store)
 
 ## Requirements
-* All linked assets are free.
-* They don't have to be open source.
+* All linked assets must be free.
+* They do not have to be open source.
 * They have to contain scripts. Pure art assets are not allowed.
 * They are allowed to contain art assets.
-* They should work with the latest release of Unity.
+* They should work with the latest stable release of Unity or have an update in the works.
 
 ## Rules
 * You are allowed to suggest links to your own assets.
-* Look through all the other links and suggestions before subbmitting yours, to ensure yours is not a duplicate.
+* Look through all the other links and suggestions before submitting your resource to ensure that the list stays free of duplicates.
 
 ## Link Suggestions
-* You can suggest a link to a free asset over [here](https://github.com/michidk/Unity-Script-Collection/issues/1).
+* Please create a pull request containing your addition.
 
 ## Pull Requests
 * Make a new pull request for each suggestion.
 * Use the following format: \[name\]\(link\) - short description
-* Keep the descriptions simple as possible..
+* Keep the descriptions as simple and as short as possible.
 
 Thank you for your help!