Nuclei wagon README.md update

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In addition to today's commit:

- The README.md update

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\u003cdetails\u003e
\u003csummary\u003ePrevious big update of the 'nuclei wagon' code\u003c/summary\u003e

* The main wagon code update:
* * bug fixes
* * new method of the evPID wagon usage
* * code clean-up
* * documentation updated and expanded
* The post-processing macro update:
* * bug fixes
* * multiprocessing of the fit functions
* * automatic fits improvements/fixes
* * documentation updated and expanded

\u003c/details\u003e