Update publications list

[apdavison]

The list of publications about or using PyNN has not been updated since 2014

[Aman123lug]

@apdavison hello, i want to work on gsoc project
please tell me steps to under the code base of it
project title : Open source, cross simulator, large scale cortical models in NeuroML and PyNN

[Dronten]

i want to work on this , can you guide me sir