Adding additional directions for installing script pre-requisites

diff --git a/share/extensions/perspective.py b/share/extensions/perspective.py
index c00a8d65d846659940c0a118e22f58d62add1d0c..dda5606deb9854109f6c1742fc6e36def2e0ce8b 100755 (executable)
--- a/share/extensions/perspective.py
+++ b/share/extensions/perspective.py
@@ -24,7 +24,7 @@ try:
     from numpy import *
     from numpy.linalg import *
 except:
-    inkex.debug("Failed to import the numpy or numpy.linalg modules. These modules are required by this extension. Please install them and try again.")
+    inkex.debug("Failed to import the numpy or numpy.linalg modules. These modules are required by this extension. Please install them and try again.  On a Debian-like system this can be done with the command, sudo apt-get install python-numpy.")
     sys.exit()
 
 uuconv = {'in':90.0, 'pt':1.25, 'px':1, 'mm':3.5433070866, 'cm':35.433070866, 'pc':15.0}