Create CONTRIBUTING.md

CONTRIBUTING.md

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+# Contribution Guidelines
+
+## Adding to this list
+
+Please ensure your pull request adheres to the following guidelines:
+
+- Search previous suggestions before making a new one, as yours may be a duplicate.
+- Make sure the list is useful before submitting. That implies it has enough content and every item has a good succinct description.
+- Make an individual pull request for each suggestion.
+- Use the following format: `[List Name](link)`
+- Link additions should be added to the bottom of the relevant category.
+- New categories or improvements to the existing categorization are welcome.
+- Check your spelling and grammar.
+- Make sure your text editor is set to remove trailing whitespace.
+
+Thank you for your contributions!