Clarify that qq example can take variables

Why this macro is an example here to begin with is that it works for any
inputs, not only numbers.  This clarifies that.

Author: anko

doc/how-macros-work.markdown

@@ -108,8 +108,8 @@ like
 Unquote (`,`) also has a cousin called unquote-splicing `,@` which can insert
 an array of stuff all at once.
 
-For example, if you want to create a shorthand `mean` for calculating the mean
-of some numbers, you could do
+For example, if you want to create a shorthand `mean` for creating the
+expression necessary to calculate the mean of some variables, you could do
 
 <!-- !test in mean macro -->
 
@@ -128,18 +128,18 @@ of some numbers, you could do
       ; Return a division of the sum of the arguments by the total
       (return `(/ (+ ,@args) ,total))))
 
-    (mean 1 2 3)
+    (mean 1 2 a)
 
-which effectively creates the eslisp code `(/ (+ 1 2 3) 3)` that compiles to JS
+which effectively creates the eslisp code `(/ (+ 1 2 a) 3)` that compiles to JS
 as—
 
 <!-- !test out mean macro -->
 
-    (1 + (2 + 3)) / 3;
+    (1 + (2 + a)) / 3;
 
 If we had used the plain unquote (`,`) instead of unquote-splicing (`,@`), we'd
-have gotten `(/ (+ (1 2 3)) 3)` which would compile to nonsense JS, as eslisp
-would think `(1 2 3)` was a function call when `1` isn't a function.
+have gotten `(/ (+ (1 2 a)) 3)` which would compile to nonsense JS, as eslisp
+would think `(1 2 a)` was a function call when `1` isn't a function.
 
 If you don't want to use `quasiquote`/`` ` `` & co., and think it's clearer for
 your use-case to just work with objects, you can still always do that.