Copyedit of the CMS 2020 Chapter

[tunetheweb]

Progress on #1432

I made the following changes:

• Moved the "goal of this chapter" section into the Introduction as otherwise looked like we had two intros
• Change tables to HTML to allow numeric formatting
• Normalised Smart Quotes as per Use of typographic quotes or "smart quotes" in the Web Almanac #1485 and changed "it's" to "it is"
• Removed some use of semi-colons that I felt were separate sentences to improve readability
• Created a "Chrome User Experience Report" heading to better group and differentiate the CrUX and Lighthouse data
• Add @rviscomi 's more positive spin as discussed in 2020 CMS Chapter #1513 (comment)
• Fixed and added more links
• Removed labels from two graphs from 1 axis for readability (included new fallback images in this PR).
• Removed the "unedited" flag! 🎉

This version of the chapter is staged here: https://20201203t160104-dot-webalmanac.uk.r.appspot.com/en/2020/cms

@alexdenning this is the last stage and then the chapter is complete and ready to publish for next week's launch. So if you could review the changes to make sure you're comfortable with them!

In particular it would be helpful for you to review:

• The plugin graph added at request in the last PR
• @rviscomi 's more positive spin on LCP
• The SEO section I added in place of Accessibility in the last PR

[alexdenning]

@bazzadp @rviscomi many thanks, and apologies for being slow – been very busy with work this week. I've had a look through and that all looks good to go, so no further suggestions from me! Cheers.