ENH/ add howfairis badge to README.md

[Moritz-Alexander-Kern]

This PR adds a badge, indicating Elephants compliance with the fair-software.eu recommendations.

For this howfairis 0.14.2 was run on https://github.com/NeuralEnsemble/elephant

Output:

Checking compliance with fair-software.eu...
url: https://github.com/NeuralEnsemble/elephant
(1/5) repository
      ✓ has_open_repository
(2/5) license
      ✓ has_license
(3/5) registry
      × has_ascl_badge
      × has_bintray_badge
      × has_conda_badge
      × has_cran_badge
      × has_crates_badge
      × has_maven_badge
      × has_npm_badge
      ✓ has_pypi_badge
      × has_rsd_badge
      × is_on_github_marketplace
(4/5) citation
      × has_citation_file
      × has_citationcff_file
      ✓ has_codemeta_file
      ✓ has_zenodo_badge
      ✓ has_zenodo_metadata_file
(5/5) checklist
      ✓ has_core_infrastructures_badge

Calculated compliance: ● ● ● ● ●

It seems you have not yet added the fair-software.eu badge to your README.md. You can do so by pasting the following snippet:

[![fair-software.eu](https://img.shields.io/badge/fair--software.eu-%E2%97%8F%20%20%E2%97%8F%20%20%E2%97%8F%20%20%E2%97%8F%20%20%E2%97%8F-green)](https://fair-software.eu)

Python package to check conditions and create a badge
https://github.com/fair-software/howfairis

Project homepage:
https://fair-software.eu/

[coveralls]

Coverage: 86.755% (+0.3%) from 86.418% when pulling a542aff on INM-6:enh/howfairis_badge into afbda28 on NeuralEnsemble:master.

[Moritz-Alexander-Kern]

part of HiRSE_PS hackathon

[Moritz-Alexander-Kern]

build wheels