Add Dart entry to glossary

src/data/glossary.yml

@@ -20,6 +20,26 @@
   labels:
     - "ui"
     - "design"
+
+- term: "Dart"
+  short_description: |-
+    A programming language for fast apps on any platform.
+  long_description: |-
+    Dart is an approachable, portable, and performant language designed
+    for full-stack app development. It offers sound null safety,
+    a strong type system, and compiles to native machine code
+    for mobile, desktop, and backend, as well as JavaScript or WebAssembly
+    for the web. While Dart is the foundation of Flutter,
+    it is also used for building command-line tools, servers,
+    and other applications.
+  related_links:
+    - text: "Dart language site"
+      link: "https://dart.dev"
+      type: "external"
+  labels:
+    - "dart"
+    - "fundamentals"
+    - "language"
 
 - term: "Embedder"
   short_description: |-