message: fix: CONTRIBUTING invalid discord server invite link
diff: # Contributing
  - Read the [style guide](#style-guide).
  -- Ask for help on the [official Discord server](https:)
  +- Ask for help on the [official Discord server](https://discord.gg/5vBgXk3UcZ)
  - If you are going to work on an issue, mention so in the issue comments before
  you start working on the issue.
  - If you are going to work on a new feature, create an issue and discuss with
  