Mention in README.md the need for the iftex package and how to get it.

diff --git a/README.md b/README.md
index 28fad2b63bb10de1b3ce09cc418348ea6b0c84ee..eadb3a6e19b8b1bc6b0fd2a62914f7233aabb2a7 100644 (file)
--- a/README.md
+++ b/README.md
@@ -53,12 +53,17 @@ guide from a command prompt, like this:
 
        make html
 
-For building the PDF version, you need a reasonably recent installation of
-TeX Live.  Release 2014 will do.  You will also need the Emerald font
-package from https://www.ctan.org/tex-archive/fonts/emerald/.  This cannot
-be installed with `tlmgr`, nor does it seem to be packaged by the usual
-Linux or BSD distributions.  Scripts for installing and uninstalling
-Emerald are provided in the `tools` directory.  When you're ready, type
+For building the PDF version, you need a reasonably recent installation 
+of TeX Live.  Release 2014 will do.  You will also need the iftex 
+package, which may or may not be automatically installed.  For Debian 
+and Debian-derived systems, the "texlive-generic-extra" package will 
+take care of this.
+
+You will also need the Emerald font package from 
+https://www.ctan.org/tex-archive/fonts/emerald/.  This cannot be 
+installed with `tlmgr`, nor does it seem to be packaged by the usual 
+Linux or BSD distributions.  Scripts for installing and uninstalling 
+Emerald are provided in the `tools` directory.  When you're ready, type 
 this:
 
        make latexpdf