Typos in extended description best practices

[jonaslil]

@clapierre @gregoriopellegrino

In addition to the issues discussed in yesterday's call, I noticed a few typos:

Section 2. Recommendations
... while the web browsers, EPUB reading systems and assistive technologies catch-up.
-> catch up (without a hyphen)

Section 2.1 Recommended technique
and appendix -> an appendix

Section 2.3 Deprecated technique
especially on the people with cognitive disabilities
-> especially on people with cognitive disabilities
(not a typo, but "the" sounds a bit odd)