Add Shell Tags on Code Blocks

[sullo]

Add shell tags on all code blocks to do better syntax highlighting for the command line examples.

This can be done simply by changing
```
{shell commands}

to

```shell
{shell commands}

For examples, see:

• https://www.mkdocs.org/user-guide/writing-your-docs/#fenced-code-blocks
• https://stackoverflow.com/questions/20303826/highlight-bash-shell-code-in-markdown-files