docs: fix broken contributing documentation link

Update the contributing link in CONTRIBUTING.md from the broken
https://jumpstarter.dev/contributing/ to the correct
https://jumpstarter.dev/main/contributing.html

Author: evakhoni

CONTRIBUTING.md

@@ -4,4 +4,4 @@ Thank you for your interest in contributing to Jumpstarter, we are an open
 community and we welcome contributions.
 
 For a complete contribution guide, please refer to our
-[documentation](https://jumpstarter.dev/contributing/).
+[documentation](https://jumpstarter.dev/main/contributing.html).