config: Make Markdown canonical

Also:

* Update the link to Go bindings after 7bf06d5 (source and schema:
  differentiate with examples, 2015-12-18, opencontainers#276).
* Add a reference to the JSON Schema after cdcabde (schema: JSON
  Schema and validator for `config.json`, 2016-01-19, opencontainers#313).

It's pretty clear that the Go bindings cannot be canonical on their
own, because they do not define limits (e.g. the 0 through 512 range
for FileMode).  The JSON Schema is closer, but still does not cover
everything (e.g. "a directory must exist at root.path").  Both the Go
bindings and the JSON Schema could grow to cover the full spec by
adding that sort of thing to comments and descriptions, but that's not
how things seem to be working now.

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

config.md

@@ -1,7 +1,7 @@
 # Container Configuration file
 
 The container's top-level directory MUST contain a configuration file called `config.json`.
-For now the canonical schema is defined in [config.go](config.go) and [config_linux.go](config_linux.go), but this will be moved to a formal JSON schema over time.
+The canonical schema is defined in this document, but there is a JSON Schema in [`schema/schema.json`](schema/schema.json) and Go bindings in [`specs-go/config.go`](specs-go/config.go).
 
 The configuration file contains metadata necessary to implement standard operations against the container.
 This includes the process to run, environment variables to inject, sandboxing features to use, etc.