Emphasize tab completion. (#1497)

Author: bkmgit

instructors/instructor-notes.md

@@ -141,6 +141,8 @@ as long as learners using Windows do not run into roadblocks such as:
   remain in view: [https://github.com/rgaiacs/swc-shell-split-window](https://github.com/rgaiacs/swc-shell-split-window).
 
 - Tab completion sounds like a small thing: it isn't.
+  Be sure to explain when you use tab completion while typing,
+  doing this often will allow learners to go faster and remind them of a useful technique.
   Re-running old commands using `!123` or `!wc`
   isn't a small thing either,
   and neither are wildcard expansion and `for` loops.