Polishing style guide (#6489)

* Polishing style guide

In preparation for the docs sprint, thought this could use a lot of polish.

Questions I could use extra eyes on @jlengstorf  @calcsam @m-allanson :
- how to make this shorter! It's crazy long. And it'd be cool if it could be downloaded as a printable pdf or something
- Wondering if our examples of good articles are good enough (under What are Guide Articles?)
- Wondering if the ## Format of a doc ought to be pulled into a new standalone doc (and possibly have real content with commentary inline or something)
- Are the rules about plagiarism reasonable (under ## search for content)?

* couple edits

* updated headers

* Filled out all templates

Need help formatting code examples within code examples

```
markdown stuff

```shell
code
``` <--how do I make sure this doesn't close out the first three backticks?

more markdown stuff
```

* ToC

* Added section on titles & headers

* example of commas gone awry

* updated plugin template

* consistent headers

* formatting fixes

* wording edits

Author: shannonbux