Add Trackarr to docs

[RaneyDazed]

Added page to apps for trackarr, ref to index and mkdocs.yml. Added a link to a config sample from the original wiki.

• [x] App documentation page created
• [x] Reference added in docs/sandbox/index.md
• [x] Reference added in mkdocs.yml

[RaneyDazed]

Closes #164

[owine]

Closes #164

Put this in the body of the PR description rather than an additional comment

[RaneyDazed]

Oh ok will do. I wasn't aware. I'll keep it in mind.