inferUserDocsDirectory causes performance and permission issues

[haoqunjiang]

• I confirm that this is an issue rather than a question.

Bug report

Steps to reproduce

cd /
vuepress -v

What is expected?

Output the version number

What is actually happening?

The command would either be stuck or throw an EACESS error.

Other relevant information

It's caused by this function:

vuepress/packages/vuepress/lib/handleUnknownCommand.js

Lines 55 to 62 in 4ddf552

	async function inferUserDocsDirectory (cwd) {
	const paths = await globby([
	'**/.vuepress/config.js',
	'!node_modules'
	], {
	cwd,
	dot: true
	})

There are several problems with this approach:

1. For global commands such as --version, --help, this detection is redundant;
2. Should have error handling if permission issue encountered;
3. There's performance bottleneck in globby if used in a large directory (say, the user home directory), should output a progress indicator in that case (e.g. "Searching for documentation under the current directory…").