Contribution guide for Issue and PR

[wusatosi]

I was originally going to take this, but since I am focusing my time on inplace vector for Jan, I would love if someone can contribute something to get us started.

Goal: Provide a clear and intuitive contributor's guide for Pull Requests and Issue Creation. Utilize GitHub's Issue Template and Pull Request Template

Components:

• Preferably both PR and issue template should be adopted from industry standard guidelines. But a clear and concise custom written guideline set would be fantastic as well.
• Must include a link to code of conduct.
• The guideline should provide a clear structure for reporting Issues/ providing PR.
• The guideline should minimize the amount of clutter it will show when viewing as a maintainer/ reviewer (tip: you can hide guidelines in comments so only the PR author would see them when proposing the PR).
• The guideline should encourage PR author to check if their change is in compliance to the beman standard.

Recommendations for PR guideline:

• The guideline should encourage small & incremental PR

Recommendations for issue guideline:

• The guideline should discourage link dump/ log dump without context.
• The guideline should encourage use of labels.

Potential reference:

• Writing good CL descriptions by Google

For tracking:

• Issue template
• PR template

[wusatosi]

Include in contribution guide for README:

1. Makesure the added info does not impact readability