Adjust how README.md refers into some of its examples.

In GitHub-flavored Markdown's fenced code blocks, Markdown formatting
is turned off and therefore surrounding underscores don't cause
italics.  So, change the text near the some examples to refer to
"underscored" words instead of to italicized words.
Format some SQL arguments correctly in a README.md example.

In the example of how to add a new user via SQL, the user's first name
and last name are also going to be inserted, so put underscores around
them too.
Merge pull request #25 from OpenTechStrategies/readme-formatting-fixes

Formatting fixes to README.md.