docs: add findBy query type docs.

Reference testing-library/dom-testing-library#224

Author: Kent C. Dodds

docs/api-queries.md

@@ -26,9 +26,26 @@ present.
 
 ### queryAllBy
 
-`queryAllBy*`queries return an array of all matching nodes for a query, and
+`queryAllBy*` queries return an array of all matching nodes for a query, and
 return an empty array (`[]`) if no elements match.
 
+### findBy
+
+`findBy*` queries return a promise which resolves when an element is found which
+matches the given query. The promise is rejected if no element is found after
+a default timeout of `4500`ms.
+
+> Note, this is a simple combination of `getBy*` queries and
+> [`waitForElement`](/docs/api-async#waitforelement). The `findBy*` queries
+> accept the `waitForElement` options as the last argument. (i.e.
+> `findByText(container, 'text', queryOptions, waitForElementOptions)`)
+
+### findAllBy
+
+`findAllBy*` queries return a promise which resolves to an array of elements when
+any elements are found which match the given query. The promise is rejected if no
+elements are found after a default timeout of `4500`ms.
+
 ## Options
 
 The argument to a query can be a _string_, _regular expression_, or _function_.