update readme and prepare release 1.2.3

Author: ghislainp

CHANGELOG.md

@@ -12,7 +12,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Changed
 
 
-## [v1.2.1]
+## [v1.2.3]
 ### Added
 
 	- implement a new diagonalisation method in DORT to avoid numerical instabilities, especially in active mode. It can be activated with rtsolver_options=dict(diagonalization_method="shur") in make_model. If good results are reported, this may become the default option as it seems as fast as the direct, origianl, eigenvalue solver.

README.md

@@ -9,6 +9,53 @@ with examples in the ['smrt-model' github organization](https://github.com/smrt-
 
 If you want to try without installing anything on your computer, use free mybinder.org notenooks: [![Binder](https://mybinder.org/badge.svg)](https://mybinder.org/v2/gh/smrt-model/smrt/master?filepath=examples/iba_onelayer.ipynb)
 
+Quick Installation
+--------------------
+
+To install the latest stable release:
+
+```console
+pip install smrt
+```
+
+Alternatively, the latest developments are available using:
+
+```console
+pip install git+https://github.com/smrt-model/smrt.git
+```
+
+or by ['manual installation'](https://smrt-model.science/getstarted.html).
+
+
+A simple example
+--------------------
+
+An example to calculate the brightness temperature from a one-layer snowpack.
+
+```python
+
+from smrt import make_snowpack, sensor_list, make_model
+
+# create a snowpack
+snowpack = make_snowpack(thickness=10.,   # snowpack depth in m
+                         microstructure_model="sticky_hard_spheres",
+                         density=320.0,   # density in kg/m3
+                         temperature=260, # temperature in Kelvin
+                         radius=100e-6)   # scatterers raidus in m
+
+# create the sensor (AMSRE, channel 37 GHz vertical polarization)
+radiometer = sensor_list.amsre('37V')
+
+# create the model including the scattering model (IBA) and the radiative transfer solver (DORT)
+m = make_model("iba", "dort")
+
+# run the model
+result = m.run(radiometer, snowpack)
+
+print(result.TbV())
+
+```
+
 
 License information
 --------------------
@@ -29,4 +76,4 @@ Other contributions
  - Marion Leduc-Leballeur
  - Mai Winstrup
  - Carlo Marin
-
+ - Justin Murfitt