Update permissions.md to fix garden path sentences

[edmundlam]

Description

When reading this particular documentation page, I had to re-read these two sentences twice because they are like garden-path sentences. The reader is lured into a parse that turns out to be a dead end or yields a clearly unintended meaning.

For example, the reader can be led down the wrong path by combining If any permission check fails with an exceptions...:

[If any permission check fails an exceptions.PermissionDenied or exceptions.NotAuthenticated exception] [will be raised,] ??? [and the main body of the view will not run.]

Adding the comma clarifies the clauses in the sentence and will make it unambiguous from the first read-through:

[If any permission check fails], [an exceptions.PermissionDenied or exceptions.NotAuthenticated exception will be raised], [and the main body of the view will not run.]

Same issue for the second modified sentence, with a small typo fix.

[tomchristie]

Sure thing. Thanks Edmund.

[edmundlam]

Thanks!