add raven-hydro to tox config, update installation.rst

Author: Zeitsperre

docs/installation.rst

@@ -57,10 +57,16 @@ Then, from your python environment, run:
 
     .. code-block:: console
 
-        python -m pip install ravenpy[gis]
+        python -m pip install ravenpy[gis,raven-hydro]
 
 If desired, the core functions of `RavenPy` can be installed without its GIS functionalities as well. This implementation of RavenPy is much lighter on dependencies and can be installed easily with `pip`, without the need for `conda` or `virtualenv`.
 
+    .. code-block:: console
+
+        python -m pip install ravenpy[raven-hydro]
+
+Finally, if you wish to provide your own `Raven` binary, you can install `RavenPy` without installing the `raven-hydro` package:
+
     .. code-block:: console
 
         python -m pip install ravenpy

tox.ini

@@ -58,6 +58,7 @@ passenv =
 extras =
     dev
     gis
+    raven-hydro
 download = true
 install_command =
     python -m pip install --no-user {opts} {packages}