driver doc updates

Signed-off-by: Evan Hazlett <ejhazlett@gmail.com>

docs/DRIVER_SPEC.md

@@ -1,5 +1,3 @@
-> DRAFT
-
 # Machine Driver Specification v1
 This is the standard configuration and specification for version 1 drivers.
 
@@ -13,6 +11,9 @@ for Docker Machine.
 ## Base Operating System
 The provider must offer a base operating system supported by the Docker Engine.
 
+Currently Machine requires Ubuntu for non-Boot2Docker machines.  This will
+change in the future.
+
 ## API Access
 We prefer accessing the provider service via HTTP APIs and strongly recommend
 using those over external executables.  For example, using the Amazon EC2 API
@@ -83,3 +84,129 @@ If you want to use a third party library to interact with the provider, you
 will need to make sure it is compliant with the Docker license terms (non-GPL).
 For more information, contact a project maintainer.
 
+# Implementation
+The following describes what is needed to create a Machine Driver.
+
+As mentioned, please review the [Driver Interface](https://github.com/docker/machine/blob/master/drivers/drivers.go#L23) for full details.
+
+## Definition
+All drivers use a struct for its basic definition:
+
+```
+type Driver struct {
+    MachineName       string
+    IPAddress         string
+    SSHUser           string
+    SSHPort           int
+    CaCertPath        string
+    PrivateKeyPath    string
+    DriverKeyPath     string
+    SwarmMaster       bool
+    SwarmHost         string
+    SwarmDiscovery    string
+    storePath         string
+}
+```
+
+Each driver must then use an `init` func to "register" the driver:
+
+```
+func init() {
+    drivers.Register("drivername", &drivers.RegisteredDriver{
+        New:            NewDriver,
+        GetCreateFlags: GetCreateFlags,
+    })
+}
+```
+
+## Flags
+Driver flags are used for provider specific customizations.  To add flags, use
+a `GetCreateFlags` func.  For example:
+
+```
+func GetCreateFlags() []cli.Flag {
+    return []cli.Flag{
+        cli.StringFlag{
+            EnvVar: "DRIVERNAME_TOKEN",
+            Name:   "drivername-token",
+            Usage:  "Provider access token",
+        
+        },
+        cli.StringFlag{
+            EnvVar: "DRIVERNAME_IMAGE",
+            Name:   "drivername-image",
+            Usage:  "Provider Image",
+            Value:  "ubuntu-14-04-x64",
+        },
+    }
+}
+```
+
+You will then need to implement the various methods defined in the Driver
+interface:
+
+```
+// AuthorizePort authorizes a port for machine access
+AuthorizePort(ports []*Port) error
+
+// Create a host using the driver's config
+Create() error
+
+// DeauthorizePort removes a port for machine access
+DeauthorizePort(ports []*Port) error
+
+// DriverName returns the name of the driver as it is registered
+DriverName() string
+
+// GetIP returns an IP or hostname that this host is available at
+// e.g. 1.2.3.4 or docker-host-d60b70a14d3a.cloudapp.net
+GetIP() (string, error)
+
+// GetMachineName returns the name of the machine
+GetMachineName() string
+
+// GetSSHHostname returns hostname for use with ssh
+GetSSHHostname() (string, error)
+
+// GetSSHKeyPath returns key path for use with ssh
+GetSSHKeyPath() string
+
+// GetSSHPort returns port for use with ssh
+GetSSHPort() (int, error)
+
+// GetSSHUsername returns username for use with ssh
+GetSSHUsername() string
+
+// GetURL returns a Docker compatible host URL for connecting to this host
+// e.g. tcp://1.2.3.4:2376
+GetURL() (string, error)
+
+// GetState returns the state that the host is in (running, stopped, etc)
+GetState() (state.State, error)
+
+// GetProviderType returns whether the instance is local/remote
+GetProviderType() provider.ProviderType
+
+// Kill stops a host forcefully
+Kill() error
+
+// PreCreateCheck allows for pre-create operations to make sure a driver is ready for creation
+PreCreateCheck() error
+
+// Remove a host
+Remove() error
+
+// Restart a host. This may just call Stop(); Start() if the provider does not
+// have any special restart behaviour.
+Restart() error
+
+// SetConfigFromFlags configures the driver with the object that was returned
+// by RegisterCreateFlags
+SetConfigFromFlags(flags DriverOptions) error
+
+// Start a host
+Start() error
+
+// Stop a host gracefully
+Stop() error
+```