docs: add "How to Build Shield Documentation"

[kenjis]

Description

• add "How to Build Shield Documentation"

Checklist:

• Securely signed commits
• [] Component(s) with PHPDoc blocks, only if necessary or adds value
• [] Unit testing, with >80% coverage
• [] User guide updated
• [] Conforms to style guide

[datamweb]

We use Material for MkDocs for implementation. It is better to add the description in this section that includes the line as follows.
https://squidfunk.github.io/mkdocs-material/getting-started/

[kenjis]

Added.

[datamweb]

Command mkdocs gh-deploy is also good for manual implementation if there is a problem. Of course, I think it needs administrator access.

[kenjis]

Added.

[datamweb]

We have previously named the files as follows.
how_to_build_docs.md

[kenjis]

Done.

[datamweb]

Thank you! 🥀