MB-15466-Update readme instructions

[NamibiaTorres]

The purpose of this PR is to add sections to the README about testing and updating the documentation so that it informs engineers who may need to make changes to the docs.

[ronaktruss]

Thanks for adding this! This has been information that has been passed along the grapevine for a while so it's nice to finally codify it.

Preface: For nits feel free to address the ones that you actually agree with. If you're on the fence you don't need to make the changes.

General nit: I think all of the headers should have an empty line after and code-block should have an empty line before and after. These seem to be fairly common suggestions across different markdown style guides. (If we really want to enforce these we should leverage automation and include it as part of the build process. Fwiw, your editor might have a pluggin that enables quick fixes for this. There are also cli tools for this. Eg. https://github.com/markdownlint/markdownlint and https://github.com/DavidAnson/markdownlint.)

[kctruss]

💖 This additional information is really useful, thank you for adding it!