[beta] Added documentation for the useMemo() API reference. (#4928)

* Documentation for useMemo API

* updated

* Update useMemo.md

* Expand useMemo ref

* tweaksg

* oops

Co-authored-by: Dan Abramov <dan.abramov@gmail.com>

beta/src/content/apis/react/index.md

@@ -349,7 +349,9 @@ useInsertionEffect(() => {
 Return a memoized callback.
 
 ```js
-const memoizedCallback = useCallback(callback, [...deps]);
+const handleClick = useCallback(() => {
+  doSomething(a, b);
+}, [a, b]);
 ```
 
 </YouWillLearnCard>
@@ -359,7 +361,9 @@ const memoizedCallback = useCallback(callback, [...deps]);
 Return a memoized value.
 
 ```js
-const memoizedValue = useMemo(() => value, [...deps]);
+const value = useMemo(() => {
+  return calculateValue(a, b);
+}, [a, b]);
 ```
 
 </YouWillLearnCard>

beta/src/sidebarReference.json

@@ -130,8 +130,7 @@
             },
             {
               "title": "useMemo",
-              "path": "/apis/react/useMemo",
-              "wip": true
+              "path": "/apis/react/useMemo"
             },
             {
               "title": "useReducer",