docs: added pip and anaconda installation

docs/source/install/index.rst

@@ -1,11 +1,19 @@
 Installation
 ============
 
-To install Grond, first install its prerequisites
+Grond is compatible with Python 2 and 3.
 
-* `Pyrocko`_ - required
+The installtion depends on:
+
+* `Pyrocko`_ - required, waveform and GNSS modelling
 * `Kite`_ - optional, needed for InSAR data modelling
 
+Other dependencies are:
+
+* `NumPy <https://www.numpy.org/>`_
+* `SciPy <https://scipy.org/>`_
+* `Matplotlib <https://matplotlib.org/>`_
+
 Next, install the Grond library and command line program with
 
 .. code-block :: sh
@@ -15,6 +23,29 @@ Next, install the Grond library and command line program with
     sudo python3 setup.py install
 
 
+With PIP
+--------
+
+Installation through pip:
+
+.. code-block :: sh
+
+    pip install pyrocko
+    pip install git@https://github.com/pyrocko/grond.git
+
+
+With Anaconda
+-------------
+
+Pyrocko's pre-build Anaconda packages are available online,
+grond is installed through pip.
+
+
+.. code-block :: sh
+    conda install -c pyrocko pyrocko
+    pip install git@https://github.com/pyrocko/grond.git
+
+
 Updating
 --------
 

src/apps/grond.py

@@ -6,10 +6,14 @@ import sys
 import os.path as op
 import logging
 from optparse import OptionParser, OptionValueError
+import grond
 
-from pyrocko import util, marker
+try:
+    from pyrocko import util, marker
+except ImportError:
+    print('Pyrocko is required for grond!'
+          'Go to https://pyrocko.org for installtion instructions.')
 
-import grond
 
 logger = logging.getLogger('grond.main')
 km = 1e3