Add guildline for writing podman V2 CLI commands

Signed-off-by: Jhon Honce <jhonce@redhat.com>

cmd/podmanV2/README.md

@@ -0,0 +1,113 @@
+# Adding a podman V2 commands
+
+## Build podman V2
+
+```shell script
+$ cd $GOPATH/src/github.com/containers/libpod/cmd/podmanV2
+```
+If you wish to include the libpod library in your program,
+```shell script
+$ go build -tags 'ABISupport' .
+```
+The `--remote` flag may be used to connect to the Podman service using the API.
+Otherwise, direct calls will be made to the Libpod library.
+```shell script
+$ go build -tags '!ABISupport' .
+```
+The Libpod library is not linked into the executable.
+All calls are made via the API and `--remote=False` is an error condition.
+
+## Adding a new command `podman manifests`
+```shell script
+$ mkdir -p $GOPATH/src/github.com/containers/libpod/cmd/podmanV2/manifests
+```
+Create the file ```$GOPATH/src/github.com/containers/libpod/cmd/podmanV2/manifests/manifest.go```
+```go
+package manifests
+
+import (
+    "github.com/containers/libpod/cmd/podmanV2/registry"
+    "github.com/containers/libpod/pkg/domain/entities"
+    "github.com/spf13/cobra"
+)
+
+var (
+    // podman _manifests_
+    manifestCmd = &cobra.Command{
+        Use:               "manifest",
+        Short:             "Manage manifests",
+        Long:              "Manage manifests",
+        Example:           "podman manifests IMAGE",
+        TraverseChildren:  true,
+        PersistentPreRunE: preRunE,
+        RunE:              registry.SubCommandExists, // Report error if there is no sub command given
+    }
+)
+func init() {
+    // Subscribe command to podman
+    registry.Commands = append(registry.Commands, registry.CliCommand{
+        // _podman manifest_ will support both ABIMode and TunnelMode
+        Mode:    []entities.EngineMode{entities.ABIMode, entities.TunnelMode},
+        // The definition for this command
+        Command: manifestCmd,
+    })
+    // Setup cobra templates, sub commands will inherit
+    manifestCmd.SetHelpTemplate(registry.HelpTemplate())
+    manifestCmd.SetUsageTemplate(registry.UsageTemplate())
+}
+
+// preRunE populates the image engine for sub commands
+func preRunE(cmd *cobra.Command, args []string) error {
+    _, err := registry.NewImageEngine(cmd, args)
+    return err
+}
+```
+To "wire" in the `manifest` command, edit the file ```$GOPATH/src/github.com/containers/libpod/cmd/podmanV2/main.go``` to add:
+```go
+package main
+
+import	_ "github.com/containers/libpod/cmd/podmanV2/manifests"
+```
+
+## Adding a new sub command `podman manifests list`
+Create the file ```$GOPATH/src/github.com/containers/libpod/cmd/podmanV2/manifests/inspect.go```
+```go
+package manifests
+
+import (
+    "github.com/containers/libpod/cmd/podmanV2/registry"
+    "github.com/containers/libpod/pkg/domain/entities"
+    "github.com/spf13/cobra"
+)
+
+var (
+    // podman manifests _inspect_
+    inspectCmd = &cobra.Command{
+        Use:     "inspect IMAGE",
+        Short:   "Display manifest from image",
+        Long:    "Displays the low-level information on a manifest identified by image name or ID",
+        RunE:    inspect,
+        Example: "podman manifest DEADBEEF",
+    }
+)
+
+func init() {
+    // Subscribe inspect sub command to manifest command
+    registry.Commands = append(registry.Commands, registry.CliCommand{
+        // _podman manifest inspect_ will support both ABIMode and TunnelMode
+        Mode:    []entities.EngineMode{entities.ABIMode, entities.TunnelMode},
+        // The definition for this command
+        Command: inspectCmd,
+        Parent:  manifestCmd,
+    })
+
+    // This is where you would configure the cobra flags using inspectCmd.Flags()
+}
+
+// Business logic: cmd is inspectCmd, args is the positional arguments from os.Args
+func inspect(cmd *cobra.Command, args []string) error {
+    // Business logic using registry.ImageEngine
+    // Do not pull from libpod directly use the domain objects and types
+    return nil
+}
+```