clarified description of doc-string

outline/functions.md

@@ -18,7 +18,7 @@ In this code:
 
 * `defn` specifies that we are defining a function.
 * `triple` is the name of this function.
-* The string on the next line is the documentation for the function. This is optional.
+* The string on the next line is the documentation for the function, which explains what the function does. This is optional.
 * `[x]` is the list of arguments. We have one argument called `x`.
 * `(+ x x x)` is the _body_ of the function. This is what executes when we use this function.