Fix standalone docs in README

[kelnos]

Description

The README contains a brief note about running Mycroft standalone (without home.mycroft.ai), but the docs were very incomplete and somewhat outdated.

How to test

n/a

Contributor license agreement signed?

CLA [x] (Whether you have signed a CLA - Contributor Licensing Agreement

[devs-mycroft]

Hello, @kelnos, thank you for helping with the Mycroft project! We welcome everyone
into the community and greatly appreciate your help as we work to build an AI
for Everyone.

To protect yourself, the project, and users of Mycroft technologies we require
a Contributor Licensing Agreement (CLA) before accepting any code
contribution. This agreement makes it crystal clear that along with your
code you are offering a license to use it within the confines of this project.
You retain ownership of the code, this is just a license.

Please visit https://mycroft.ai/cla to initiate this one-time signing. Thank
you!

[forslund]

Thanks for the update, it looks good. I added a suggestion of including a link to the STT setup documentation.

[forslund]

Thanks for the update! Looks good now. Merging.