docs: add global option for uninstall

[m4rch3n1ng]

running npm uninstall --help or npm help uninstall does not list [-g|--global] as an option, even though it is an option and is mentioned as a possibility in

cli/docs/lib/content/commands/npm-uninstall.md

Lines 30 to 34 in 173bc89

	In global mode (ie, with `-g` or `--global` appended to the command),
	it uninstalls the current package context as a global package.
	`--no-save` is ignored in this case.

this pr adds that option to the docs