Add Slack to list of GitHub-created apps

[megbird]

Issue overview

As noted in a related issue:

The one thing we could do for core docs is add the Slack app to the list of GitHub-created integrations in "GitHub extensions and integrations."

Slack isn't on our list of GitHub-created apps in "GitHub extensions and integrations."

Let's add the Slack integration to the article and also 💅 existing content:

• Fix the formatting in the TOC
• ✂️ the repetitive "To streamline your workflow..." sentences under each header

The Slack app is already live so we can update the article anytime; because this is a small enhancement to existing content, I'm tracking this as a user-reported issue.

Products affected by this issue

• Dotcom
• GitHub Enterprise end user docs
• GitHub Enterprise admin docs
• Desktop

/cc @github/product-docs-core https://github.com/github/ecosystem-integrations/issues/147

[ParkourKarthik]

I would love to pick this up. I believe that I should wait for docs team review.

[janiceilene]

@ParkourKarthik Feel free to open a pull request and address this issue ✨ Thanks for contributing 🎉

[felicitymay]

@ParkourKarthik raised #542 to fix this issue - thanks 😄

I've just merged the PR and the updated content is already public: Project management tools. ✨