Permission fixes

[benwoo1110]

About this pull request

Fix some docs and types typo related to the permissions PR.

Checklist

• I've checked this pull request runs on Python 3.6.X.
• This fixes something in Issues.
  • Issue:
• This adds something new.
• There is/are breaking change(s).
• (If required) Relevant documentation has been updated/added.
• This is not a code change. (README, docs, etc.)

[quirky-bluejay]

Something i was thinking about. Would it be a good idea to document the format of permissions for the command decorators?
It's mostly mentioned in getting started, but imo you shouldn't have to look in guides to find that out.

[benwoo1110]

Yea the example code should be quite clear that it's a dictionary. Also I improved the docs string for them in the above commit.

Also there is a sentence on it in getting started:

The key being the guild to apply permissions on, and value being the list of permissions to apply.

[eunwoo1104]

LGTM

[eunwoo1104]

Merging, thank you for contributing!