Improve FAQ on importing wallet into metamask

[rampall]

• How do I get the node's wallet's private key (use-case for Desktop app)?
• How do I import the swarm private key to metamask?
• Where can I find my password?

The FAQ answers to the above questions can be significantly improved to provide clear solutions specific to their OS and their node setup (Desktop, CLI, Service). Something along the lines of this guide might be more helpful - https://hackmd.io/@rampall/HJUKcwT56