Added a note about correct usage of async matchers

lib/jasmine-core/jasmine.js

@@ -3722,7 +3722,29 @@ getJasmineRequireObj().Expectation = function(j$) {
   });
 
   /**
-   * Asynchronous matchers.
+   * Asynchronous matchers that operate on an actual value which is a promise,
+   * and return a promise.
+   *
+   * Note: Specs must await the result of each async matcher, return the
+   * promise returned by the matcher, or return a promise that's derived from
+   * the one returned by the matcher. Otherwise the matcher will not be
+   * evaluated before the spec completes.
+   *
+   * @example
+   * // Good
+   * await expectAsync(aPromise).toBeResolved();
+   * @example
+   * // Good
+   * return expectAsync(aPromise).toBeResolved();
+   * @example
+   * // Good
+   * return expectAsync(aPromise).toBeResolved()
+   *  .then(function() {
+   *    // more spec code
+   *  });
+   * @example
+   * // Bad
+   * expectAsync(aPromise).toBeResolved();
    * @namespace async-matchers
    */
   function AsyncExpectation(options) {

src/core/Expectation.js

@@ -43,7 +43,29 @@ getJasmineRequireObj().Expectation = function(j$) {
   });
 
   /**
-   * Asynchronous matchers.
+   * Asynchronous matchers that operate on an actual value which is a promise,
+   * and return a promise.
+   *
+   * Note: Specs must await the result of each async matcher, return the
+   * promise returned by the matcher, or return a promise that's derived from
+   * the one returned by the matcher. Otherwise the matcher will not be
+   * evaluated before the spec completes.
+   *
+   * @example
+   * // Good
+   * await expectAsync(aPromise).toBeResolved();
+   * @example
+   * // Good
+   * return expectAsync(aPromise).toBeResolved();
+   * @example
+   * // Good
+   * return expectAsync(aPromise).toBeResolved()
+   *  .then(function() {
+   *    // more spec code
+   *  });
+   * @example
+   * // Bad
+   * expectAsync(aPromise).toBeResolved();
    * @namespace async-matchers
    */
   function AsyncExpectation(options) {