Update README

Author: Fückert, Oliver

README.md

@@ -1,6 +1,11 @@
 # ACI2DOT
 
-aci2dot converts JSON formatted Cisco ACI policy files or snippets to a DOT graph format.
+aci2dot converts JSON formatted Cisco ACI policy files or snippets to a [DOT](https://en.wikipedia.org/wiki/DOT_(graph_description_language)) graph format.
+
+It requires Python 3. [Graphwiz](https://www.graphviz.org) is not required as long as the option --dot is not used.
+When [Graphwiz](https://www.graphviz.org) is installed `--dot {svg,png,pdf}` will also render the graph in the respective format.
+
+`--write` creates a config file `.aci2dot` in the current directory, which allows for modification of the graph, node and edge properties.
 
 ```
 ./aci2dot.py --help