Create note from unix pipe stream only with `import` command

[Yukaii]

The mixed-use of oclif multi command/single command causes flag parsing weird sometimes.

hackmd-cli/src/index.ts

Lines 20 to 30 in 1f8f30f

	if (pipeString) {
	try {
	const url = await APIClient.newNote(pipeString)
	this.log(`Your note is available at ${url}`)
	} catch (err) {
	this.error(err)
	}
	} else {
	await multiRun()
	process.exit(0)
	}

I want to move the pipe import command under import.ts command.

[Yukaii]

This command is now replaced with notes create or team notes create command.