Add a SlashCommand example

[Sitois]

Summary

This pull request is to add an skash command example because a lot of people are asking how to do that.

General Info

• [ x] If code changes were made then they have been tested.
  • [ ] I have updated the documentation to reflect the changes.
• [ ] This PR fixes an issue (please put issue # in summary).
• [x ] This PR adds something new (e.g. new method or parameters).
• [ ] This PR is a breaking change (e.g. methods or parameters removed/renamed)
• [ x] This PR is not a code change (e.g. documentation, README, ...)

[dolfies]

Sorry I didn't get a chance to properly review this, I've been very busy recently :(

Having an example like this is good but this implementation has a couple issues so I'll probably end up doing it alone