Improve examples and help in several commands

[rfay]

The Problem/Issue/Bug:

Some older commands had no examples at all. Some help text was a bit out of date.

How this PR Solves The Problem:

Add examples to most commands.

Manual Testing Instructions:

Automated Testing Overview:

Related Issue Link(s):

Release/Deployment notes:

[AlexCreamer]

This look like very nice addition. It seems to give more of an incentive to run some of the commands to see what the examples are. And with the examples being better. The import-files one stumped me, but with the --src example it might help some people. **** Perhaps adding that in some text that import-files supports .sql would be good. Preferably through whatever users will easily see. Not sure if using "long" text would make people easily see it since they may not see that from the command line.

[rfay]

Thanks for taking a look @AlexCreamer ! The "short" text is shown when you just type "ddev", the long text when you type ddev help <command> or ddev command -h