docs: create reusable content for how to install guide and the tutorial

[IronCore864]

Create some reusable content for the tutorial, how-to-install doc, pebble install verification, and references.

Changes:

• make installing and verifying pebble content reusable
• refactor the how-to-install doc to use reusable content
• refactor the tutorial to use reusable content
• mark the pebble help reference doc with the reference link
• toc of the reference page now is visible

[IronCore864]

In a sync with Anne, there is no more comment from her side. Merging now.