config: Consistent Markdown/Go wording for 'mounts'

I've replaced the old MAY 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.

Signed-off-by: W. Trevor King <[email protected]>

Author: wking

config.md

@@ -39,7 +39,7 @@ For example, if an implementation is compliant with version 1.0.1 of the spec, i
 
 ## Mounts
 
-You MAY add array of mount points inside container as `mounts`.
+**`mounts`** (array, optional) configures additional mounts (on top of [`root`](#root-configuration)).
 The runtime MUST mount entries in the listed order.
 The parameters are similar to the ones in [the Linux mount system call](http://man7.org/linux/man-pages/man2/mount.2.html).
 

specs-go/config.go

@@ -14,7 +14,7 @@ type Spec struct {
 	Root Root `json:"root"`
 	// Hostname configures the container's hostname.
 	Hostname string `json:"hostname,omitempty"`
-	// Mounts profile configuration for adding mounts to the container's filesystem.
+	// Mounts configures additional mounts (on top of Root).
 	Mounts []Mount `json:"mounts,omitempty"`
 	// Hooks are the commands run at various lifecycle events of the container.
 	Hooks Hooks `json:"hooks"`