runtime: Add 'version' to the state.json example

The version field was added while 180df9d (Add runtime state
configuration and structs, 2015-07-29, opencontainers#87) was in-flight [1], and it
missed getting documented in the example.

[1]: opencontainers#87 (comment)

Signed-off-by: W. Trevor King <wking@tremily.us>

runtime.md

@@ -27,6 +27,7 @@ This is provided so that consumers can find the container's configuration and ro
 
 ```json
 {
+    "version": "0.2.0",
     "id": "oc-container",
     "pid": 4422,
     "root": "/containers/redis"