rewrite 'help cmdname' text slightly

- fixes a grammatical error
- remove a trailing whitespace
- quotes the provided command in the result
- make consistent response text across 'found' / 'notfound' cases
- indent actual commands in response by 2 characters to distinguish the list from pages/etc
Merge pull request #27 from floatingatoll/patch-2

rewrite 'help cmdname' text slightly