Add update_interval to sensor and binary_sensor exposes

[jeremysherriff]

Addresses #141

[jeremysherriff]

I can't find a way to submit a PR for the gitbook docs page

[bkbilly]

Thank you for this PR!

It seems that there are some formating issues and an issue with the self.discovery_info in lines 24 and 31.
You can run this procedure yourself using pre-commit command.

As for the documentation, it exists under the branch gh-pages so you could fork it and create a PR there.
I haven't done this before, but I don't see any reason you will have any issue.

[jeremysherriff]

Yeah I see two linting issues, my github-foo isn't strong so just trying to work out how I add more edits :)

[bkbilly]

You just need to push a new commit to your branch and it will show here.