[readme] add section on bare `nvm install` #819

Job	Run time
Cygwin nvm install	6m 17s
MSYS fail prefix nvm install	4m 18s
MSYS nvm install (--lts)	1m 2s
MSYS nvm install (--default 12)	1m 24s
WSL nvm install (Debian, --lts)	1m 46s
WSL nvm install (Debian, --lts, script)	1m 59s
WSL nvm install (Debian, 14)	3m 25s
MSYS nvm install (--no-progress 10)	1m 49s
WSL nvm install (Debian, 14, script)	2m 21s
WSL nvm install (Debian, 12)	2m 19s
WSL nvm install (Debian, 12, script)	2m 27s
WSL nvm install (Debian, 11)	3m 5s
WSL nvm install (Debian, 11, script)	2m 9s
WSL nvm install (Debian, 10)	2m 45s
WSL nvm install (Debian, 10, script)	2m 31s
WSL nvm install (Alpine, --lts)	56s
WSL nvm install (Alpine, --lts, script)	1m 2s
WSL nvm install (Alpine, 14)	44s
WSL nvm install (Alpine, 14, script)	1m 22s
WSL nvm install (Alpine, 12)	40s
WSL nvm install (Alpine, 12, script)	1m 31s
WSL nvm install (Alpine, 11)	1m 0s
WSL nvm install (Alpine, 11, script)	53s
WSL nvm install (Alpine, 10)	1m 7s
WSL nvm install (Alpine, 10, script)	1m 13s
WSL nvm install (Ubuntu-18.04, --lts)	2m 59s
WSL nvm install (Ubuntu-18.04, --lts, script)	3m 46s
WSL nvm install (Ubuntu-18.04, 14)	4m 42s
WSL nvm install (Ubuntu-18.04, 14, script)	5m 4s
WSL nvm install (Ubuntu-18.04, 12)	3m 45s
WSL nvm install (Ubuntu-18.04, 12, script)	4m 6s
WSL nvm install (Ubuntu-18.04, 11)	4m 14s
WSL nvm install (Ubuntu-18.04, 11, script)	3m 34s
WSL nvm install (Ubuntu-18.04, 10)	5m 0s
WSL nvm install (Ubuntu-18.04, 10, script)	6m 47s
tests, on windows	1s
	1h 34m 3s

Provide feedback