Add installation instructions

doc/index.rst

@@ -1,22 +1,18 @@
-.. TrollImage documentation master file, created by
-   sphinx-quickstart on Mon Dec  2 09:40:29 2013.
-   You can adapt this file completely to your liking, but it should at least
-   contain the root `toctree` directive.
-
-Welcome to TrollImage's documentation!
-======================================
+TrollImage
+==========
 
 .. image:: _static/hayan.png
 
 Get the source code here_ !
 
-.. _here: http://github.com/mraspaud/trollimage
+.. _here: http://github.com/pytroll/trollimage
 
 Contents:
 
 .. toctree::
    :maxdepth: 2
 
+   installation
    image
    xrimage
    colorspaces

doc/installation.rst

@@ -0,0 +1,95 @@
+============
+Installation
+============
+
+Trollimage is available from conda-forge (via conda), PyPI (via pip), or from
+source (via pip+git). The below instructions show how to install stable
+versions of trollimage or from the source code.
+
+Conda-based Installation
+========================
+
+Trollimage can be installed into a conda environment by installing the package
+from the conda-forge channel. If you do not already have access to a conda
+installation, we recommend installing
+`miniconda <https://docs.conda.io/en/latest/miniconda.html>`_ for the smallest
+and easiest installation.
+
+The commands below will use ``-c conda-forge`` to make sure packages are
+downloaded from the conda-forge channel. Alternatively, you can tell conda
+to always use conda-forge by running:
+
+.. code-block:: bash
+
+    $ conda config --add channels conda-forge
+
+In a new conda environment
+--------------------------
+
+We recommend creating a separate environment for your work with trollimage. To
+create a new environment and install trollimage all in one command you can
+run:
+
+.. code-block:: bash
+
+    $ conda create -c conda-forge -n my_trollimage_env python trollimage
+
+You must then activate the environment so any future python or
+conda commands will use this environment.
+
+.. code-block::
+
+    $ conda activate my_trollimage_env
+
+This method of creating an environment with trollimage (and optionally other
+packages) installed can generally be created faster than creating an
+environment and then later installing trollimage and other packages (see the
+section below).
+
+In an existing environment
+--------------------------
+
+.. note::
+
+    It is recommended that when first exploring trollimage, you create a new
+    environment specifically for this rather than modifying one used for
+    other work.
+
+If you already have a conda environment, it is activated, and would like to
+install trollimage into it, run the following:
+
+.. code-block:: bash
+
+    $ conda install -c conda-forge trollimage
+
+Pip-based Installation
+======================
+
+Trollimage is available from the Python Packaging Index (PyPI). A sandbox
+environment for ``trollimage`` can be created using
+`Virtualenv <http://pypi.python.org/pypi/virtualenv>`_.
+
+To install the `trollimage` package and the minimum amount of python dependencies:
+
+.. code-block:: bash
+
+    $ pip install trollimage
+
+Install from source
+===================
+
+To install directly from github into an existing environment (pip or conda-based):
+
+.. code-block:: bash
+
+    $ pip install git+https://github.com/pytroll/trollimage.git
+
+If you have the ``git`` command installed this will automatically download the
+source code and install it into the current environment. If you would like to
+modify a local copy of trollimage and see the effects immediately in your
+environment use the below command instead. This command should be run from the
+root your cloned version of the git repository (where the ``setup.py`` is located):
+
+.. code-block::
+
+    $ pip install -e .