Small edits for operator-editing-code.xml

Follow conventions to place a space after the prompt.
Add missing space between text and URL.
Capitalize all items in lists for consistency and add periods
at the end.
Use username consistently instead of user, yourusername etc.
Fix markup to follow conventions, especially about filenames and links.

Change-Id: I99c9b9ed1b95fd8b0f9b42ddd7a205eda0f11431
Merge "Small edits for operator-editing-code.xml"