clarify retry docs. Closes #936

Author: Alexander Early

README.md

@@ -1445,30 +1445,40 @@ result (if any) of the final attempt.
 
 __Arguments__
 
-* `opts` - Can be either an object with `times` and `interval` or a number. `times` is how many attempts should be made before giving up. `interval` is how long to wait inbetween attempts. Defaults to {times: 5, interval: 0}
-  * if a number is passed in it sets `times` only (with `interval` defaulting to 0).
+* `opts` - Can be either an object with `times` and `interval` or a number.
+  * `times` - The number of attempts to make before giving up.  The default is `5`.
+  * `interval` - The time to wait between retries, in milliseconds.  The default is `0`.
+  * If `opts` is a number, the number specifies the number of times to retry, with the default interval of `0`. 
 * `task(callback, results)` - A function which receives two arguments: (1) a `callback(err, result)`
   which must be called when finished, passing `err` (which can be `null`) and the `result` of
   the function's execution, and (2) a `results` object, containing the results of
   the previously executed functions (if nested inside another control flow).
 * `callback(err, results)` - An optional callback which is called when the
   task has succeeded, or after the final failed attempt. It receives the `err` and `result` arguments of the last attempt at completing the `task`.
 
-The [`retry`](#retry) function can be used as a stand-alone control flow by passing a
-callback, as shown below:
+The [`retry`](#retry) function can be used as a stand-alone control flow by passing a callback, as shown below:
 
 ```js
+// try calling apiMethod 3 times
 async.retry(3, apiMethod, function(err, result) {
     // do something with the result
 });
 ```
 
 ```js
+// try calling apiMethod 3 times, waiting 200 ms between each retry 
 async.retry({times: 3, interval: 200}, apiMethod, function(err, result) {
     // do something with the result
 });
 ```
 
+```js
+// try calling apiMethod the default 5 times no delay between each retry 
+async.retry(apiMethod, function(err, result) {
+    // do something with the result
+});
+```
+
 It can also be embedded within other control flow functions to retry individual methods
 that are not as reliable, like this: