update README

README.md

@@ -6,12 +6,18 @@ This is the Coq development of the [Iris Project](http://iris-project.org).
 
 This version is known to compile with:
 
- - Coq 8.5pl2
- - [Ssreflect 1.6](https://github.com/math-comp/math-comp/releases/tag/mathcomp-1.6)
+ - Coq 8.5pl3
+ - Ssreflect 1.6
+ - A development version of [Iris](https://gitlab.mpi-sws.org/FP/iris-coq/)
+
+The easiest way to install the correct versions of the dependencies is through
+opam.  Once you got opam set up, just run `make build-dep` to install the right
+versions of the dependencies.  When the dependencies change, just run `make
+build-dep` again.
 
 For development, better make sure you have a version of Ssreflect that includes
 commit ad273277 (no such version has been released so far, you will have to
-fetch the development branch yourself). Iris compiles fine even without this
+fetch the development branch yourself).  Iris compiles fine even without this
 patch, but proof bullets will only be in 'strict' (enforcing) mode with the
 fixed version of Ssreflect.  If you are using opam, you can easily get a fixed
 version by running
@@ -20,14 +26,7 @@ version by running
  
 ## Building Instructions
 
-Run the following command to build the full development:
-
-    make
-
-The development can then be installed as the Coq user contribution `iris` by
-running:
-
-    make install
+Run `make` to build the full development.
 
 ## Structure