improve contribution guidelines

contributing.md

@@ -6,19 +6,23 @@ Please note that this project is released with a [Contributor Code of Conduct](c
 
 Ensure your pull request adheres to the following guidelines:
 
+- **If you just created something, wait at least 30 days before submitting.** This is to give it some time to mature and ensure it's not just a publish-and-forget type of project.
+- Keep in mind that the list is very mature by now, so the bar of getting something accepted is high. Only submit something unique and generally useful. The world (and this list) doesn't need yet another ORM or framework. For CLI tools, the bar is especially high, and unless it's something very awesome, I would suggest submitting to [awesome-cli-apps](https://github.com/aharris88/awesome-cli-apps) instead.
+- If you submit a project that is similar to an existing project in the list, argument how it's better.
 - Search previous suggestions before making a new one, as yours may be a duplicate.
 - Suggested packages should be tested and documented.
 - Make an individual pull request for each suggestion.
 - Use the following format: `[package](link) - Description.`
 - Additions should be added to the bottom of the relevant category.
-- New categories, or improvements to the existing categorization are welcome.
 - Link to the GitHub repo, not npmjs.com.
 - Keep descriptions short and simple, but descriptive.
 - Don't mention `Node.js` in the description as it's implied.
 - Start the description with a capital and end with a full stop/period.
+- Don't start the description with `A` or `An`.
 - Check your spelling and grammar.
 - Make sure your text editor is set to remove trailing whitespace.
 - The pull request should have a useful title and include a link to the package and why it should be included.
+- New categories or improvements to the existing categorization are welcome, but should be done in a separate pull request.
 
 Thank you for your suggestion!