lifecycle: Mention runtime.json

As discussed earlier [1,2].  I'm in favor of rolling it back into
config.json [3], but we aren't there yet [4].

[1]: opencontainers#231 (comment)
[2]: https://github.com/opencontainers/specs/pull/231/files#r46735828
[3]: https://groups.google.com/a/opencontainers.org/forum/#!topic/dev/0QbyJDM9fWY
     Subject: Single, unified config file (i.e. rolling back specs#88)
     Date: Wed, 4 Nov 2015 09:53:20 -0800
     Message-ID: <20151104175320.GC24652@odin.tremily.us>
[4]: https://github.com/opencontainers/specs/blob/4a63e81a807edec3d67ed2b6bd99a6c2b288676f/bundle.md#container-format

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

runtime.md

@@ -38,8 +38,8 @@ This is provided so that consumers can find the container's configuration and ro
 The lifecycle describes the timeline of events that happen from when a container is created to when it ceases to exist.
 
 1. OCI compliant runtime is invoked by passing the bundle path as argument.
-2. The container's runtime environment is created according to the configuration in config.json.
-   Any updates to config.json after container is running do not affect the container.
+2. The container's runtime environment is created according to the configuration in `config.json` and `runtime.json`.
+   Any updates to `config.json` or `runtime.json` after container is running do not affect the container.
 3. The container's state.json file is written to the filesystem under /run/opencontainer/<runtime>/containers/<id>/.
 4. The prestart hooks are invoked by the runtime.
    If any prestart hook fails, then the container is stopped and the lifecycle continues at step 8.