File useful_error_message.patch of Package singularity

Subject: Add an useful error message when the user doesn't belong to the singularity group
Date: 2019.12.19

diff -Nrua src/github.com/sylabs/singularity/internal/pkg/util/starter/starter.go src/github.com/sylabs/singularity/internal/pkg/util/starter/starter.go
--- a/src/github.com/sylabs/singularity/internal/pkg/util/starter/starter.go	2019-12-03 23:07:06.000000000 +0100
+++ b/src/github.com/sylabs/singularity/internal/pkg/util/starter/starter.go	2019-12-18 00:48:35.670565337 +0100
@@ -90,7 +90,7 @@
 		return fmt.Errorf("while initializing starter command: %s", err)
 	}
 	err := unix.Exec(c.path, []string{name}, c.env)
-	return fmt.Errorf("while executing %s: %s", c.path, err)
+	return fmt.Errorf("while executing %s: %s\nPlease read /usr/share/doc/packages/singularity/README.SUSE to get help\n", c.path, err)
 }
 
 // Run executes the starter binary and returns once starter