docs: broken links pointing to /api

[HeCorr]

Description

As warned by Docusaurus when building the docs:

Exhaustive list of all broken links found:
- Broken link on source page path = /next/contributing/:
   -> linking to /api
- Broken link on source page path = /next/usage/:
   -> linking to /api#exit-codes
- Broken link on source page path = /contributing/:
   -> linking to /api
- Broken link on source page path = /usage/:
   -> linking to /api#exit-codes

I am able to fix the Usage links but I'm not sure what the Contributing links should actually point to:

If you added a new field, command or flag, ensure that you add it to the [API Reference](https://taskfile.dev/api).

Should they point to Schema Reference or CLI Reference? Both seem equally relevant to that phrase.

[pd93]

Hi @HeCorr, thanks for spotting. I've pushed a fix to both the latest and next versions of the docs in f5121de.