docs: Improved Consistency in Fork Instructions Update CONTRIBUTING.md

[mdqst]

Please go through the following checklist

• The PR title and commit messages adhere to guidelines here: https://github.com/spaceandtimelabs/sxt-proof-of-sql/blob/main/CONTRIBUTING.md. In particular ! is used if and only if at least one breaking change has been introduced.
• I have run the ci check script with source scripts/run_ci_checks.sh.

Description

While reviewing the contribution guide, I noticed a minor inconsistency in the formatting of the "Fork the Repository" section. Specifically, the sentence "Add the original repository as a remote (optional but recommended)." ended with a period, whereas other similar instructions use a colon for clarity and flow.

I've replaced the period with a colon to ensure uniformity throughout the guide.
This small tweak helps maintain a consistent style and makes the instructions easier to follow.

[iajoiner]

@mdqst Thanks for your contribution! Hmm this actually makes it less consistent. If you can make an improvement (such as fixing a typo) I will approve. Otherwise I will close it in a week.