[guide] clarify function spacing in 18.3

Per airbnb#668.

Author: ljharb

README.md

@@ -1500,7 +1500,7 @@ Other Style Guides
     });
     ```
 
-  - [18.3](#18.3) <a name='18.3'></a> Place 1 space before the opening parenthesis in control statements (`if`, `while` etc.). Place no space before the argument list in function calls and declarations.
+  - [18.3](#18.3) <a name='18.3'></a> Place 1 space before the opening parenthesis in control statements (`if`, `while` etc.). Place no space between the argument list and the function name in function calls and declarations.
 
     eslint rules: [`space-after-keywords`](http://eslint.org/docs/rules/space-after-keywords.html), [`space-before-keywords`](http://eslint.org/docs/rules/space-before-keywords.html).