add instructions for development version

README.md

@@ -14,6 +14,18 @@ If you don't have `opam`, you can install it following the [how to install opam]
 
 If you can't or don't want to use `opam`, you can build the package with `dune build -p owi @install` but you'll first have to install the dependencies by yourself. You can find the list of dependencies in the [dune-project] file.
 
+### Development version
+
+To get the development version:
+
+```shell-session
+$ git clone [email protected]:OCamlPro/owi.git
+$ cd owi
+$ opam install . --deps-only
+$ dune build -p owi @install
+$ dune install
+```
+
 ## Quickstart
 
 ### Concrete interpretation