add contribution guidelines

CONTRIBUTING.md

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+# Contribution Guidelines
+
+To start a discussion, simply create an issue.
+
+You can add links through pull requests, ensure your pull request adheres to the following guidelines:
+
+- Search previous suggestions before making a new one, as yours may be a duplicate.
+- Make an individual pull request for each suggestion.
+- Use the following format:
+ - for GitHub repos : `[author/reponame](link) - Description.` `.
+ - for websites : `[Website](link) [language] - Description.` `[language]` is optional if english.
+ - for articles : `[Author](link) [language] - (publication year) Description.` `[language]` is optional if english.
+- Keep link descriptions short and simple, but descriptive.
+- Check your spelling and grammar.