Update installation instructions

README.md

@@ -3,8 +3,13 @@
 This package implements the Julia interface to the real-time framework of Tao
 (a *Toolkit for Adaptive Optics*).
 
+
 ## Installation
 
+[TAO real-time libraries](https://git-cral.univ-lyon1.fr/tao/tao-rt) and
+[Tao.jl](https://git-cral.univ-lyon1.fr/tao/Tao.jl) Julia package must have
+been installed.  Follow instructions there.
+
 Two environment variables, `TAO_INCDIR` and `TAO_LIBDIR`, have to be defined to
 indicate where are TAO header files and TAO libraries.  They can be defined
 in your shell or in Julia.   For instance for a Bourne-like shell: