config: config: Consistent Markdown/Go wording for 'annotations'

I've replaced the old OPTIONAL with our usual:

  (<type>, <optional|required>)

to get the property name first, since that translates more directly
into a Go comment that godoc will like.

The new Go comment is much shorter, dropping "unstructured" (because
the Markdown says "structured or unstructured") and "set by external
tools..." (because *everything* in the configuration JSON is set by
external-to-the-runtime tools).

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

config.md

@@ -322,7 +322,7 @@ The semantics are the same as `Path`, `Args` and `Env` in [golang Cmd](https://g
 
 ## Annotations
 
-This OPTIONAL property contains arbitrary metadata for the container.
+**`annotations`** (object, optional) contains arbitrary metadata for the container.
 This information MAY be structured or unstructured.
 Annotations are key-value maps.
 

specs-go/config.go

@@ -18,7 +18,7 @@ type Spec struct {
 	Mounts []Mount `json:"mounts,omitempty"`
 	// Hooks configures callbacks for container lifecycle events.
 	Hooks Hooks `json:"hooks"`
-	// Annotations is an unstructured key value map that may be set by external tools to store and retrieve arbitrary metadata.
+	// Annotations contains arbitrary metadata for the container.
 	Annotations map[string]string `json:"annotations,omitempty"`
 
 	// Linux is platform specific configuration for Linux based containers.