add a bit of space around the left-hand rule

I think the IDE would look better and be a bit easier to read if a couple of white pixels were added on each side of the left-hand rule (just to the left of the first character in the code line.

The issue names no files or tests; start by locating the IDE editor code that draws the left-hand rule and inspect how its horizontal spacing is defined. Confirm the change visually in the Arduino IDE, with a small amount of space on both sides of the rule.

Written by the indexing model from the issue text.