Update help docs with required arguments

[manish-makwana]

Most commands require the app name, which was not previously shown in the help documentation. The documentation has been updated based on either trial and error with gocan v0.2.3, or the examples provided.

This caused me quite a bit of confusion as the app didn't explain what the expected argument was - I had to delve into the code to understand what was needed when trying to use gocan hotspots. Hopefully this makes it clearer for new users.

Note that there are some commands that may still require <app-name>, but I didn't see an example for them or didn't use them myself to verify the correct syntax.