Update download/installation instructions to clarify the dependencies, and encourage the use of conda. Also updated the link to Xavier's QGis plugin repo. (#87)

Author: neilflood

INSTALL.txt

@@ -2,6 +2,9 @@
 WARNING: To install python-fmask it is strongly  recommended to use the conda forge
 pre-built binaries. Only install from source if you absolutely must.
 
+The code requires RIOS, GDAL, numpy and scipy. These must be installed, preferrably
+using a package manager such as conda.
+
 
 To install python-fmask from the source code bundle, use the following commands
 

doc/source/index.rst

@@ -151,9 +151,9 @@ corresponds to which wavelength band.
 
 Downloads
 ---------
-Get the source as a bundle from `GitHub <https://github.com/ubarsc/python-fmask/releases>`_.
-Release notes for each version can be read in :doc:`releasenotes`. To install from source,
-read the INSTALL.txt file included inside the source bundle.
+This code relies heavily on GDAL, numpy, scipy and RIOS. These packages must be
+installed for anything to work. For this reason, we recommend that you install using
+a package manager, which will build a complete environment with everything required.
 
 Pre-built binary `Conda <https://github.com/conda-forge/miniforge>`_ packages are available
 under the 'conda-forge' channel. Once you have installed
@@ -170,10 +170,24 @@ python-fmask is also available as::
 
     spack install py-python-fmask
 
+The source can be downloaded directly as a bundle from
+`GitHub <https://github.com/ubarsc/python-fmask/releases>`_.
+Release notes for each version can be read in :doc:`releasenotes`. To install from source,
+read the INSTALL.txt file included inside the source bundle.
+
+Please note that python-fmask is *not* available from the PyPI repository. This is
+because it depends on the GDAL library, which is also not available there, and must
+be installed by some other means, such as conda. If one is using conda for GDAL, one
+may as well use it for python-fmask, too. While it is technically possible to bundle
+the GDAL binaries into a PyPI distribution, this carries grave risks of version
+conflicts if any other package does the same thing, and is best avoided.
+
 Applications that use python-fmask
 ----------------------------------
 
-* `Cloud Masking <https://smbyc.bitbucket.io/qgisplugins/cloudmasking/>`_: It  is a Qgis plugin for cloud masking the Landsat (4, 5, 7 and 8) products using different process and filters such as Fmask, Blue Band, Cloud QA, Aerosol and Pixel QA.
+* `Cloud Masking <https://github.com/SMByC/CloudMasking>`_: It is a Qgis plugin for cloud masking
+  the Landsat (4, 5, 7 and 8) products using different process and filters such as Fmask, Blue Band,
+  Cloud QA, Aerosol and Pixel QA.
 
 Issues
 ------