introduce --compatibility (noop) for backward ... compatibility

Signed-off-by: Nicolas De Loof <[email protected]>

cmd/compose/compose.go

@@ -148,7 +148,9 @@ func (o *projectOptions) addProjectFlags(f *pflag.FlagSet) {
 	f.StringVar(&o.EnvFile, "env-file", "", "Specify an alternate environment file.")
 	f.StringVar(&o.ProjectDir, "project-directory", "", "Specify an alternate working directory\n(default: the path of the Compose file)")
 	f.StringVar(&o.WorkDir, "workdir", "", "DEPRECATED! USE --project-directory INSTEAD.\nSpecify an alternate working directory\n(default: the path of the Compose file)")
+	f.Bool("compatibility", false, "DEPRECATED")
 	_ = f.MarkHidden("workdir")
+	_ = f.MarkHidden("compatibility")
 }
 
 func (o *projectOptions) toProjectName() (string, error) {