doc: note JavaScript is not single threaded

Honestly I appreciate the effort and don't have time to go over the whole thing but there are plenty of inaccuracies in this document.

This PR fixes the first one I noticed - JavaScript as a language is _not_ single threaded. Nor has it ever been, and multithreaded JavaScript execution dates back at least 10-20 years

Signed-off-by: Benjamin Gruenbaum <[email protected]>

Author: benjamingr

apps/site/pages/en/learn/asynchronous-work/event-loop-timers-and-nexttick.md

@@ -8,7 +8,7 @@ layout: learn
 ## What is the Event Loop?
 
 The event loop is what allows Node.js to perform non-blocking I/O
-operations — despite the fact that JavaScript is single-threaded — by
+operations — despite the fact that a single JavaScript thread is used by default — by
 offloading operations to the system kernel whenever possible.
 
 Since most modern kernels are multi-threaded, they can handle multiple