README: removal of bitdeli badge

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
README: pypi badge fix

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
README: new About section and minor wordsmithing

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>