Added contributing guidelines.

Author: ArSn

CONTRIBUTING.md

@@ -14,7 +14,8 @@ The following is a set of guidelines for contributing to json-graph-specificatio
 
 [How Can I Contribute?](#how-can-i-contribute)
   * [Reporting Bugs](#reporting-bugs)
-
+  * [Suggesting Enhancements](#suggesting-enhancements)
+  * [Pull Requests](#pull-requests)
 
 ## Code of Conduct
 
@@ -46,4 +47,39 @@ Explain the problem and include additional details to help maintainers reproduce
 
 * **Use a clear and descriptive title** for the issue to identify the problem.
 * **Describe the exact steps which reproduce the problem** in as many details as possible. When listing steps, **don't just say what you did, but explain how you did it**.
-* **Provide specific examples to demonstrate the steps**. 
+* **Provide specific examples to demonstrate the steps**. 
+
+Include links to files or GitHub projects, or copy/pasteable snippets, which you use in those examples. If you're providing snippets in the issue, use [Markdown code blocks](https://help.github.com/articles/markdown-basics/#multiple-lines).
+* **Describe the behavior you observed after following the steps** and point out what exactly is the problem with that behavior.
+* **Explain which behavior you expected to see instead and why.**
+
+### Suggesting Enhancements
+
+This section guides you through submitting an enhancement suggestion for json-graph-specification, including completely new features and minor improvements to existing functionality. Following these guidelines helps maintainers and the community understand your suggestion and find related suggestions.
+
+When you are creating an enhancement suggestion, please [include as many details as possible](#how-do-i-submit-a-good-enhancement-suggestion). 
+
+#### How Do I Submit A (Good) Enhancement Suggestion?
+
+Enhancement suggestions are tracked as [GitHub issues](https://guides.github.com/features/issues/). Create an issue and provide the following information:
+
+* **Use a clear and descriptive title** for the issue to identify the suggestion.
+* **Provide a step-by-step description of the suggested enhancement** in as many details as possible.
+* **Provide specific examples to demonstrate the steps**. Include copy/pasteable snippets which you use in those examples, as [Markdown code blocks](https://help.github.com/articles/markdown-basics/#multiple-lines).
+* **Describe the current behavior** and **explain which behavior you expected to see instead** and why.
+
+### Pull Requests
+
+This is the main way how you can contribute to the specification. Feel free to open a pull request for your propsed changes at any time. The requirements described here have several goals:
+
+- Maintain the quality of json-graph-specification
+- Fix problems that are important to users
+- Engage the community in working toward the best possible json-graph-specification
+
+Please adhere to these requirements to have your contribution considered by the maintainers:
+
+1. Write meaningful commit messages
+2. Explain in your pull request what you are trying to achieve, and why
+3. Be open minded about suggestions or other perspectives from the maintainers and other contributors
+
+While the prerequisites above must be satisfied prior to having your pull request reviewed, the reviewer(s) may ask you to complete additional design work, tests, or other changes before your pull request can be ultimately accepted.