docs: improve contributing

[Panquesito7]

Description

• Improve contributing.
  • Mention linking to The Algorithms' website if applicable (optional). Links to their specific implementation shouldn't be removed.
  • This is very useful in case there are too many implementations in multiple languages of the same algorithm, which can be easily checked on the website.

Closes #190

Checklist

• A description of the changes in this PR is mentioned above.
• All the new and existing checks pass.
• No plagiarized, duplicated, or repetitive documentation that has been directly copied from another source.
• If it's a new explanation, it contains solid, understandable, and accessible information.
• I have read the whole contributing guidelines and agree to the Code of Conduct.

Note to reviewers