Update README.md

README.md

 # prodigy: A library for manipulation distributions through generating functions
 
+The main features are
+- python bindings
+- a purely string-based interface, no need to mess around with data structures for algebraic expression and the like
+- support for parameters (can also be used as meta symbols in second-order PGFs)
+
 ## Prerequisites
 
 GiNaC must be installed on your system.
@@ -8,4 +13,14 @@ On macOS with homebrew type
 
 ## Installation
 
+Activate the virtual environment where prodigy should be installed, then type
+
 ```pip install .```
+
+## Usage
+
+```
+import prodigy
+dist = prodigy.geometric("x", "1/2")
+e = dist.E("x")  # e becomes 2
+'''