Update readme and wrote separate readme's for packages

README.md

 pystencils
 ==========
 
+Run blazingly fast stencil codes on numpy arrays.
 
 ![alt text](doc/img/logo.png)
 
+
+Installation
+------------
+
+```bash
+export PIP_EXTRA_INDEX_URL=https://www.walberla.net/pip
+pip install pystencils[interactive]
+```
+
+Without `[interactive]` you get a minimal version with very little dependencies.
+
+All options:
+-  `gpu`: use this if nVidia GPU is available and CUDA is installed
+- `alltrafos`: pulls in additional dependencies for loop simplification e.g. libisl
+- `bench_db`: functionality to store benchmark result in object databases
+- `interactive`: installs dependencies to work in Jupyter including image I/O, plotting etc.
+- `doc`: packages to build documentation
+
+Options can be combined e.g.
+```bash
+pip install pystencils[interactive,gpu,doc]
+```    
+
+
+Documentation
+-------------
+
+Read the docs [here](http://software.pages.walberla.net/pystencils/pystencils)
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