Fix MAD-NG link

Author: jgray-19

README.md

@@ -8,7 +8,7 @@ Install using below, see [The Python Package Index (PyPi)](https://pypi.org/proj
 Familiarising yourself with pymadng
 ===================================
 
-First, we recommend familiarising yourself with MAD-NG, documentation can be found [here](https://mad.web.cern.ch/mad/releases/madng/html/). 
+First, we recommend familiarising yourself with MAD-NG, documentation can be found [here](https://madx.web.cern.ch/releases/madng/html/). 
 
 Then reading through the Low-Level Example Explained on the [pymadng documentation](https://pymadng.readthedocs.io/en/latest/) should be sufficient (alongside knowledge of MAD-NG), assuming you are not planning to use any "syntactic sugar". If you plan to use the available pythonic looking code, there are plenty of examples to look at.