syntax highlighting

[seanlerner]

This PR:

• adds syntax highlighting to the shell commands and one json output
• marks output and results as plaintext so highlighting won't be incorrectly applied
• trims trailing whitespace

This makes it easier to read the commands in various places.

In an editor (sublime):

In the terminal (using bat):

Unfortunately it doesn't change how github renders syntax highlighting for shell commends too much:

[kelseyhightower]

I might consider this in a feature version of this guide.