Minor improvements to CI page

[dstansby]

• Don't put an acronym in table of contents
• Note that GH Actions also available for private repos for free
• Link to testing page for test coverage collection recommendation
• Add a details box explaining why there are two 🟢 coverage hosting tools

[paddyroddy]

Seeing as this is the first time we are using CI, should we define it?

Suggested change

	We have many projects using GitHub CI and, it has good integration with GitHub itself, and is free for public repositories (with limited free monthly minutes for private repositories).
	We have many projects using GitHub continuous integration (CI) and, it has good integration with GitHub itself, and is free for public repositories (with limited free monthly minutes for private repositories).

[paddyroddy]

Would be nice if this page could be wrapped to 80 chars, in keeping with other pages

[dstansby]

I think if we want to enforce wrap to 80 it would be best to do via a pre-commit hook instead of having to manually edit?

[dstansby]

Thanks for catching the acronym - I edited the title of this section instead since CI is such a common acronym.

[paddyroddy]

Sure, it's slightly tricky though as links can go over - and tables. I like markdownlint.

[dstansby]

For wrapping I opened a new issue at #337