Make documentation easier for new users

[ajafff]

The current documentation is a bit hard to grasp. The main readme should describe how to start and what is necessary for users.

For users landing on a rule's documentation, there should be an easy path to find out how to get started using that rule.

Remove references to TSLint. It's EOL, so we don't need to compare to it. Maybe create a page describing how to migrate from TSLint and which rules are similar.

(Re)move all the nerdy stuff from the main readme. It adds no value for most readers.