Improve contribution guidelines

Author: alexeyzimarev

.github/ISSUE_TEMPLATE.md

@@ -1,3 +1,10 @@
+## Read this first!
+
+**Important**
+- Please do not use GitHub issues to ask question about using RestSharp.
+- Ensure to read the Get help docs page at https://restsharp.dev/get-help/ before opening an issue/ 
+- Issues not following our contribution guidelines will be marked as `invalid` and closed in three days.
+
 ## Expected Behavior
 
 

CONTRIBUTING.md

@@ -2,16 +2,17 @@ Follow these guidelines, in no particular order, to improve your chances of havi
 
 ### Before you do anything else
 
- * Before reporting an issue or creating a pull request, discuss it in the Google Group http://groups.google.com/group/restsharp
- * If you have an inquiry - ask a question on StackOverflow, tagged with `restsharp` tag.
+ * DO: Read about [getting help](https://restsharp.dev/get-help/) in the docs.
+ * DO: Follow the guidelines below when contributing.  
+ * DO: Discuss bigger change in the issue before implementing it.  
+ * DO NOT: Use issues to ask questions about using the library.
 
 ### Once a contribution is ready to be submitted
 
  * Make each pull request atomic and exclusive; don't send pull requests for a laundry list of changes.
  * Even better, commit in small manageable chunks.
  * Spaces, not tabs. Bracket style doesn't matter. Do not reformat code you didn't touch.
- * Changes to XmlDeserializer or JsonDeserializer must be accompanied by a unit test covering the change.
- * In general, changes should be accompanied by unit tests to show what was broken and how your patch fixes it.
+ * Changes should be accompanied by unit tests to show what was broken and how your patch fixes it.
  * No regions except for license header
  * Code must build for .NET 4.5.2 and .NET Standard 2.0
  * If you didn't write the code you must provide a reference to where you obtained it and preferably the license.