doc: add undici to glossary

PR-URL: nodejs#43327
Reviewed-By: Antoine du Hamel <[email protected]>
Reviewed-By: Tobias Nießen <[email protected]>
Reviewed-By: Akhil Marsonya <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>

Author: F3n67u

glossary.md

@@ -18,3 +18,5 @@ 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 alternative HTTP client used in Node.js. See more details
+  on the [undici repository](https://github.com/nodejs/undici).