DOC: Add a NEP link to all neps.

Usefull for crossreferencing and intersphinx

Here is a snippet to update it if other neps are missing it:

    In [1]: neps = !ls nep-0*
       ...: for nep in neps:
       ...:     number = nep[6:8]
       ...:     with open(nep, 'r') as f:
       ...:         data = f.read()
       ...:
       ...:     if f'.. _NEP{number}:' in data:
       ...:         continue
       ...:     with open(nep, 'w') as f:
       ...:         f.write('.. _NEP'+number+':\n')
       ...:         f.write(data)
       ...:

0 files changed, 0 insertions, 0 deletions