Improve docs for $base-font-size variable.
Improve docs for $base-font-size variable.

webmarkelov/normalize-scss,justindirose/normalize-scss,Alexdersan/normalize-scss,Alexdersan/normalize-scss,justindirose/normalize-scss,nabu1615/normalize-scss,JohnAlbin/normalize-scss,webmarkelov/normalize-scss,nabu1615/normalize-scss,JohnAlbin/normalize-scss,JohnAlbin/normalize-scss