Add code hyperlinking guidelines to CONTRIBUTING.md

[7se7en72025]

Added a "Code Hyperlinks" section to CONTRIBUTING.md. This explains a user when to use GitHub permalinks for code blocks/highlighting and when to use source links.

Summary:

Adds guideline for contributors on best practices for referencing code.

Permalinks for highlighted code/lines

Source links for general references

Fixes #141

[llrs]

Hi! Thanks for your contribution. The wording is good and it doesn't promote one mirror over others.

I wonder if in the original issue, the recommendation was meant for when adding content to the guideline or when referencing R source code on bugs and mail list discussions.

If it is the later this section might be better on the reporting_bugs chapter. Leaving open for now.

[7se7en72025]

Thank you for your feedback!

My intent with this addition was to provide contributors clear guidelines on the best practice for referencing code specifically, when to use permalinks for highlighted code/lines versus when to use source links for general references. My focus was on situations where people are contributing to the codebase, but I see how it could also apply when referencing R source code during bug reporting or mail list discussions.

If you feel this content fits better in the reporting_bugs chapter, I am happy to move it there or adjust the section as needed. Please let me know your preference!

[llrs]

I'll wait for @SaranjeetKaur opinion, as she was the one that opened the issue. Maybe it can end up on the two documents.