Minor grammar and clarity improvements in project background

[Sanika123-art]

I made small updates to the Contribution Guide to improve readability and fix minor grammar issues.

1. Fixed comma splice in project background paragraph

Original text:

The original body of work took place at a series of unconferences and various spurts of energy, today the DISCOVER-Cookbook is a living project with numerous contributors.

Updated text:

The original body of work took place at a series of unconferences and various spurts of energy. Today, the DISCOVER Cookbook is a living project with numerous contributors.

2. Improved readability of content quality sentence

Original text:

While content is the heart of the project, the quality of the content needs to remain high.

Updated text:

While content is the heart of the project, maintaining high quality is essential.

These changes are purely documentation improvements and do not alter any contribution rules or workflow.

[netlify]

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[Sanika123-art]

Note: My changes are only documentation improvements.
The Netlify deploy failed due to missing dependencies (sphinx_togglebutton) which are unrelated to my edits.
Approval from a maintainer is required to merge this PR.