Update JetBrains installation instructions

[vincentpaca]

Why:

There are minor inaccuracies on the installation instructions and also missing context that helps to find the relevant sections described in the steps.

Closes [issue link]

What's being changed (if available, include any code snippets, screenshots, or gifs):

• Add the window naming nuances for Windows and Mac
• Add the extra step to find the Plugins section as previously it just asked to find the Marketplace button at the top of the window.

Check off the following:

• I have reviewed my changes in staging (look for the "Automatically generated comment" and click the links in the "Preview" column to view your latest changes).
• For content changes, I have completed the self-review checklist.

Writer impact (This section is for GitHub staff members only):

• This pull request impacts the contribution experience
  • I have added the 'writer impact' label
  • I have added a description and/or a video demo of the changes below (e.g. a "before and after video")

[welcome]

Thanks for opening this pull request! A GitHub docs team member should be by to give feedback soon. In the meantime, please check out the contributing guidelines.

[github-actions]

Automatically generated comment ℹ️

This comment is automatically generated and will be overwritten every time changes are committed to this branch.

The table contains an overview of files in the content directory that have been changed in this pull request. It's provided to make it easy to review your changes on the staging site. Please note that changes to the data directory will not show up in this table.

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Content directory changes

You may find it useful to copy this table into the pull request summary. There you can edit it to share links to important articles or changes and to give a high-level overview of how the changes in your pull request support the overall goals of the pull request.

Source	Preview	Production	What Changed
copilot/getting-started-with-github-copilot/getting-started-with-github-copilot-in-a-jetbrains-ide.md	fpt ghec	fpt ghec

[cmwilson21]

@vincentpaca Thanks so much for opening a PR! I'll get this triaged for review ⚡

[jules-p]

Hi @vincentpaca 👋🏻 thanks so much for opening this pull request, we really appreciate your contribution. I've made a couple of small edits to the wording to align with our style guide, but otherwise I think this is looking great! I'll go ahead and merge these changes now ✨

[github-actions]

Thanks very much for contributing! Your pull request has been merged 🎉 You should see your changes appear on the site in approximately 24 hours. If you're looking for your next contribution, check out our help wanted issues ⚡