doc: add undici to glossary

Author: F3n67u

glossary.md

@@ -18,3 +18,7 @@ You may also need to check <https://chromium.googlesource.com/chromiumos/docs/+/
   primarily administrated by Matt Godbolt.
 * primordials: Pristine built-ins that are not affected by prototype pollution
   and tampering with built-ins.
+* undici: An HTTP/1.1 client, written from scratch for Node.js. Undici means
+  eleven in Italian. 1.1 -> 11 -> Eleven -> Undici. It is also a Stranger Things
+  reference. Undici is maintained within a separate repository, see more details
+  on the [undici repository](https://github.com/nodejs/undici).