Update Day 21 to completed with live demo link

Author: AngelaRead

readme.md

@@ -26,7 +26,7 @@ My solutions to [Wes Bos's JavaScript 30 Day Challenge](https://JavaScript30.com
 - [x] Day 18 - Adding Up Times with Reduce
 - [x] Day 19 - Webcam Fun - [Live Demo](https://angelaread.github.io/JavaScript30/19%20-%20Webcam%20Fun/) *(requires camera access)*
 - [ ] Day 20 - Speech Detection *(skipped - microphone input issue with remote app, will revisit)*
-- [ ] Day 21 - Geolocation
+- [x] Day 21 - Geolocation - [Live Demo](https://angelaread.github.io/JavaScript30/21%20-%20Geolocation/) *(best experienced on mobile while moving)*
 - [ ] Day 22 - Follow Along Link Highlighter
 - [ ] Day 23 - Speech Synthesis
 - [ ] Day 24 - Sticky Nav