doc: fix entryTypes type and missing link

PR-URL: nodejs#15406
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

doc/api/perf_hooks.md

@@ -202,7 +202,7 @@ const obs = new PerformanceObserver((list) => {
   obs.disconnect();
   performance.clearFunctions();
 });
-obs.observe({ entryTypes: 'function' });
+obs.observe({ entryTypes: ['function'] });
 
 // A performance timeline entry will be created
 wrapped();
@@ -655,4 +655,5 @@ require('some-module');
 ```
 
 [`timeOrigin`]: https://w3c.github.io/hr-time/#dom-performance-timeorigin
+[Async Hooks]: async_hooks.html
 [W3C Performance Timeline]: https://w3c.github.io/performance-timeline/