Add prose, JS/TS & Rust guidelines used by Unboxed and prof-education

[mikemaccana]

There's an existing CONTRIBUTING.md used by the Unboxed Course, created by James and I, and used for both the Unboxed Course and Professional Education programs. Per Slack, ideally we could delete 90% of it and just refer to the one in this repo, with some added bits.

[mikemaccana]

I've merged https://github.com/solana-foundation/developer-content/pull/199 into this one and made the following changes:

• Recommend to use the grammarly app for checking English instead of a vscode extension?
• Moved above content guidelines

I've also added a suggestion of adding Solana words to the Grammarly dictionary.

[mikemaccana]

@nickfrosty can you please check this out?

[jacobcreech]

@mikemaccana I'm not sure if it makes sense to copy over the contributing guide from unboxed to this repo. They're fundamentally different repositories.

Our time is better spent on other things since we already have a decent contributing guide.

[nickfrosty]

Yeah, I agree with Jacob

[mikemaccana]

@jacobcreech I strongly disagree that developer-content, professional-education, and solana-course are fundamentally different - please check the contents on this PR and judge for yourself. There's valuable content to ensure the quality and consistency of JS, Anchor, prose, etc., regardless of the purpose of the developer content, some of which has been needed by this repo (e.g., getting people into the habit of running Grammarly, avoiding magic numbers, using the standard multiple files layout for Anchor, etc).

Our time is better spent on other things

This saves time, rather than consumes it. The guidelines have already been created by James and I, and we use them to ensure contributors - particularly third parties - create content that will pass our PRs later. Removing these items will slow down the iteration process as we get submissions that don't match our standards and have to go back and forth in PRs for longer.

we already have a decent contributing guide.

This PR doesn't duplicate anything, it just adds what's missing. Check out the changes.

Any publication - website, blog, magazine, etc. you've ever read - has a strong style guide. It's used to create a consistent voice for the publication, and if someone is being paid to write for them, they ensure the writer reads it before they do anything else.

Short version: this is important and we need it.

[mikemaccana]

@jacobcreech we also want to get this merged before the Superteam bounty, so the new updates are consistent with recent Unboxed work.