[docs] Added docs for registry server subcommand + build fixes (#627)

Signed-off-by: Sarvesh Raj <[email protected]>

README.md

@@ -624,6 +624,16 @@ Other useful flags:
 - `--dump-raw-manifest` - Dump raw manifest for the created image index.
 - `--insecure-refs` - Allow the referenced images from insecure registry connections.
 
+#### `SERVER` SUBCOMMAND OPTIONS
+
+Starts a server which implements the [OCI API spec](https://github.com/opencontainers/distribution-spec/blob/v1.0.1/spec.md) on port 5000
+
+USAGE: `slim registry server`
+
+Other useful flags: 
+
+- `--with-referrer-api` - Enables the [referrers API endpoint](https://github.com/opencontainers/distribution-spec/blob/v1.1.0-rc3/spec.md#enabling-the-referrers-api) (OCI 1.1+)
+
 ## RUNNING CONTAINERIZED
 
 The current version of Slim is able to run in containers. It will try to detect if it's running in a containerized environment, but you can also tell Slim explicitly using the `--in-container` global flag.

pkg/app/master/command/registry/cli.go

@@ -219,17 +219,16 @@ var CLI = &cli.Command{
 			Name:  ServerCmdName,
 			Usage: ServerCmdNameUsage,
 			Action: func(ctx *cli.Context) error {
-				gcvalues, err := command.GlobalFlagValues(ctx)
-				if err != nil {
-					return err
-				}
+				gcvalues := command.GlobalFlagValues(ctx)
 
 				cparams, err := ServerCommandFlagValues(ctx)
 				if err != nil {
 					return err
 				}
 
-				xc := app.NewExecutionContext(fullCmdName(ServerCmdName), ctx.String(command.FlagConsoleFormat))
+				xc := app.NewExecutionContext(fullCmdName(ServerCmdName),
+					gcvalues.QuietCLIMode,
+					gcvalues.OutputFormat)
 				OnServerCommand(xc, gcvalues, cparams)
 				return nil
 			},