contributing.md

Ensure your pull request adheres to the following guidelines:

- Search previous suggestions before making a new one, as yours may be a duplicate.
- Suggested packages should be tested and documented.
- The pull request should have a meaningful title and include a link to the package / resource and why it's awesome.
- Make an individual pull request for each suggestion.
- Use the following format: `[resource](link) - Description by [Author](link to author)`
- Use [title-casing](http://titlecapitalization.com) (AP style).
- Additions should be added to the bottom of the relevant category.
- New categories, or improvements to the existing categorization are welcome.
- Keep descriptions short and simple, but descriptive.
- Don't mention `Flutter` in the description as it's implied.
- Start the description with a capital.
- Check your spelling and grammar.
- Make sure your text editor is set to remove trailing whitespace.

Thank you for your suggestions!