update installation instructions

docs/install.rst

@@ -1,9 +1,40 @@
 Installation
 ============
 
-For developers
---------------
+Using pip
+---------
 
+Optional but recommended step: install a conda environment::
+
+  conda create -n <cosipy_env_name> python=3.10 pip
+  conda activate <cosipy_env_name>
+
+Note: currently cosipy is not compatible with Python 3.11 and 3.12, mainly due to
+installation issues with a dependency (astromodels, see issues `#201 <https://github.com/threeML/astromodels/issues/201>`_ and `#204 <https://github.com/threeML/astromodels/issues/204>`_)
+
+Install with pip::
+  
+  pip install cosipy==0.0.2a1
+
+Note: you need to specify the alpha release 0.0.2a1, otherwise pip will fall back to
+the latest regular release (which is currently unusable). This will be updated when
+we have our next regular release.
+
+
+From source (for developers)
+----------------------------
+
+Optional but recommended step: install a conda environment::
+
+  conda create -n <cosipy_env_name> python=3.10 pip
+  conda activate <cosipy_env_name>
+
+Also optional but recommented: before installing cosipy, install the main
+dependencies from source (similar
+procedure as for cosipy below). These are histpy, mhealpy, scoords, threeml and
+astromodels. The reason is that these libraries might be changing rapidly to
+accomodate new features in cosipy. 
+
 Do the following (preferably inside a conda environment)::
 
     git clone [email protected]:cositools/cosipy.git