Fixes to the WebAssembly Threads article (#8170)
Fixes to the WebAssembly Threads article (#8170)

In the *WebAssembly Threads ready to try in Chrome 70* article,

- Added a note at the beginning of the article saying that WebAssembly threads are enabled by default in Chrome 74 for desktop (see https://www.chromestatus.com/feature/5724132452859904), and the origin trial mentioned in the article ended in Chrome 75 (see https://developers.chrome.com/origintrials/#/view_trial/-5026017184145473535).
- Fixed misplaced `_`'s meant to make a bold "pthreads" word italic.
- Fixed some misplaced/missing space.
- Added missing commas.
- Added a missing "the".
lucab85/WebFundamentals,lucab85/WebFundamentals,google/WebFundamentals,lucab85/WebFundamentals,myakura/WebFundamentals,lucab85/WebFundamentals,myakura/WebFundamentals,myakura/WebFundamentals,myakura/WebFundamentals,google/WebFundamentals,google/WebFundamentals,google/WebFundamentals