chore: update marketplace details

Author: mhanberg

package.json

@@ -17,7 +17,12 @@
     "vscode": "^1.77.0"
   },
   "categories": [
-    "Programming"
+    "Programming Languages",
+    "Linters"
+  ],
+  "keywords": [
+    "elixir",
+    "credo"
   ],
   "activationEvents": [],
   "main": "./dist/extension.js",