updated installation things with pip and conda

docs/start/installation.rst

@@ -3,19 +3,18 @@
 How to install
 ==============
 
-you can install it via
+you can install it via pip
 
 .. code-block:: bash
 
-  git clone https://github.com/ClimateClara/arc3o.git
-  pip install arc3o/
+  pip install arc3o
 
-or via
+or via conda
 
 
 .. code-block:: bash
 
-  pip install git+https://github.com/ClimateClara/arc3o.git
+  conda install -c conda-forge arc3o
 
 This package is programmed in python 3.6 and should be working with all `python
 versions > 3.6`. Additional requirements are numpy, xarray, pandas, tqdm and pathos.
@@ -27,3 +26,6 @@ We recommend to install the dependencies via
   conda install -c conda-forge pandas tqdm pathos 
 
 as they might not work well using ``pip``.
+
+If you want to work on the code, please fork this github repository: https://github.com/ClimateClara/arc3o/
+