add small note

_slides/notepad.md

@@ -48,6 +48,13 @@
 - Good for R: RStudio
 - Good for Python: Pycharm
 
+6. specify the interpreter in the first line (for terminal executability), e.g.
+- bash: `#! /bin/bash`
+- python: `#! /usr/bin/env python3`
+- r: `#!/usr/bin/env Rscript`
+> once you make the script executable (`chmod +x <script>.sh`), you can execute it directly (i.e. `./<script>.sh` instead of `bash./<script>.sh`) 
+
+
 ## Challenge exercise Day 3
 
 The pipeline we've shown you in the class was desigend to work (mostly smoothly) with the data, structure and parameters just as we've provided.