Add a doc.go file so the compose/schema/data directory can be vendored in another project, without being pruned.

Signed-off-by: Silvin Lubecki <silvin.lubecki@docker.com>

cli/compose/schema/bindata.go

@@ -1,4 +1,4 @@
-// Code generated by "esc -o bindata.go -pkg schema -private -modtime=1518458244 data"; DO NOT EDIT.
+// Code generated by "esc -o bindata.go -pkg schema -ignore .*\.go -private -modtime=1518458244 data"; DO NOT EDIT.
 
 package schema
 

cli/compose/schema/data/doc.go

@@ -0,0 +1,8 @@
+/*
+	Package data contains all the Compose file JSON schemas, starting from v3.0.
+*/
+
+//
+// +domain=docker.com
+
+package data

cli/compose/schema/schema.go

@@ -1,6 +1,6 @@
 package schema
 
-//go:generate esc -o bindata.go -pkg schema -private -modtime=1518458244 data
+//go:generate esc -o bindata.go -pkg schema -ignore .*\.go -private -modtime=1518458244 data
 
 import (
 	"fmt"