Update examples to have explicit interfaces (#203)

Author: adamspofford-dfinity

examples/icp-motoko-recipe/greeter.did

@@ -0,0 +1,3 @@
+service : {
+  greet : (name : text) -> (text) query
+}

examples/icp-motoko-recipe/icp.yaml

@@ -1,7 +1,9 @@
-canister:
+canisters:
   - name: my-canister
     recipe:
-      type: "@dfinity/motoko" 
+      type: "@dfinity/motoko"
       configuration:
         main: src/main.mo
         args: --incremental-gc
+        # optional
+        candid: greeter.did

examples/icp-rust-recipe/greeter.did

@@ -0,0 +1,3 @@
+service : {
+  greet : (name : text) -> (text) query
+}

examples/icp-rust-recipe/icp.yaml

@@ -6,6 +6,8 @@ canisters:
         # cargo package for canister (required field)
         package: icp-canister
         shrink: true
+        # optional
+        candid: greeter.did
         metadata:
           - name: "crate:version"
             value: 1.0.0