Add radix-heap pipeline

.drone.yml

@@ -19,3 +19,16 @@ steps:
       - cd algo2
       - gcc -o pairingheap pairingheap.c
       - ./pairingheap
+
+---
+kind: pipeline
+type: docker
+name: haskell
+
+steps:
+  - name: radix-heap
+    image: nixos/nix:2.11.0
+    commands:
+      - cd algo2/radix-heap
+      - stack build
+      - stack test