Document that deepEqual() uses lodash.isequal

readme.md

@@ -914,11 +914,15 @@ Assert that `value` is not equal to `expected`.
 
 ### `.deepEqual(value, expected, [message])`
 
-Assert that `value` is deep equal to `expected`.
+Assert that `value` is deep equal to `expected`. This is based on [Lodash' `isEqual()`](https://lodash.com/docs/4.17.4#isEqual):
+
+> Performs a deep comparison between two values to determine if they are equivalent.
+>
+> *Note*: This method supports comparing arrays, array buffers, booleans, date objects, error objects, maps, numbers, `Object` objects, regexes, sets, strings, symbols, and typed arrays. `Object` objects are compared by their own, not inherited, enumerable properties. Functions and DOM nodes are compared by strict equality, i.e. `===`.
 
 ### `.notDeepEqual(value, expected, [message])`
 
-Assert that `value` is not deep equal to `expected`.
+Assert that `value` is not deep equal to `expected`. The inverse of `.deepEqual()`.
 
 ### `.throws(function|promise, [error, [message]])`