add hint to use /bin/sh -e consistently (thanks, Steven!)

Signed-off-by: Nico Schottelius <nico@bento.schottelius.org>

docs/man/man7/cdist-troubleshooting.text

@@ -31,7 +31,8 @@ it does not lead to an error. And thus cdist sees the exit 0
 code of the last echo line instead of the failing command.
 
 All scripts executed by cdist carry the -e flag. 
-To prevent the above from happening, there are two solutions available:
+To prevent the above from happening, there are three solutions available,
+two of which can be used in the calling script:
 --------------------------------------------------------------------------------
 # Execute as before, but abort on failure
 sh -e "$__manifest/special"
@@ -40,6 +41,16 @@ sh -e "$__manifest/special"
 . "$__manifest/special"
 --------------------------------------------------------------------------------
 
+The third solution is to include a shebang header in every script
+you write to use the -e flag:
+
+--------------------------------------------------------------------------------
+% cat ~/.cdist/manifest/special
+#!/bin/sh -e
+...
+--------------------------------------------------------------------------------
+
+
 SEE ALSO
 --------
 - cdist(1)