Doc updates

[Sjlver]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• [-] Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe: Documentation update

What is the current behavior?

The readme was outdated in several places. There was no good description of the throttling logic.

What is the new behavior?

I've added a short description of the logic. Also, fixed some stale links and clarified some code examples.

Does this PR introduce a breaking change?

• Yes
• No

[Sjlver]

@jmcdo29 would you have time to take a look at this PR one of these days?

[jmcdo29]

From a quick view everything looks good. I might suggest we just link over to the nest docs site, but this works too. Thanks for the updates

[Sjlver]

Cool, thanks!

@jmcdo29 you'd have to do the actual merge, since I don't have write access to the repository.