Document That Users Can Self-Assign Issues

[cicoyle]

Please link to the daprbot documentation inside the contributing.md file, so that users know what Github commands they can run in this repo. Based on the dapr-bot.yml they can run the /assign to self assign issues and a few other commands in this repo.

[Shubhdeep02]

@cicoyle I will take this ticekt....
/assign

[Shubhdeep02]

#1330 fixes this one