add a draft of installation instructions for Ubuntu

README-UBUNTU.md

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+# Install prequisites
+
+```
+sudo apt-get install wget xsltproc xmlto fonts-dejavu fonts-linuxlibertine unifont ruby-full zip unzip default-jdk`
+gem install bundler
+bundle install
+
+#install epub lib:
+sudo -v && wget -nv -O- https://download.calibre-ebook.com/linux-installer.sh | sudo sh /dev/stdin
+#Xvfb and xvfb-run (fake X for calibre) or a running X server session -- MAYBE NOT ACTUALLY NEEDED
+
+sudo apt-get install python-pip
+sudo apt-get install xvfb xserver-xephyr vnc4server
+sudo pip install pyvirtualdisplay
+# optional
+sudo apt-get install python-pil scrot
+sudo pip install pyscreenshot
+
+# install Prince for your platform from https://www.princexml.com/download/ e.g.:
+wget https://www.princexml.com/download/prince_12.5-1_ubuntu18.04_amd64.deb
+sudo apt install ./prince_12.5-1_ubuntu18.04_amd64.deb
+```
+
+
+
+There might be other libs needed. Please, open an issue once you find it.
+
+# Compilation
+
+To make all the versions do:
+
+`./cll_build`
+
+The final results will end up under the build/ directory, scattered
+about in various places.  If you would like the final outputs only
+to be copied to another directory, you can use the -a option, so for example:
+
+`./cll_build -a output/`
+
+would put all the outputs in the output/ directory, whereas
+
+`./cll_build -a ~/public_html/cll_build/`
+
+would put them in your personal webspace.
+
+Running a complete build takes quite a while (like probably at least
+an hour).  To do it for just one chapter for faster testing:
+
+`./cll_build -t chapters/05.xml`
+
+This does the whole book but is also much faster:
+
+`./cll_build -t`
+
+There are many possible sub-targets as well, which are specified
+with -T, such as:
+
+`./cll_build -t -T pdf`
+
+You can get a complete list of targets via:
+
+`./cll_build -h`