algo parameter documentation

[timosachsenberg]

add to https://pyopenms.readthedocs.io/en/latest/parameter_handling.html how to getDescription in a nice way

[timosachsenberg]

also check if it makes sense to print key, value, description in

 __repr__ or  __str__

e.g., users want to write print(myParam)

def __str__(self):
  return list(zip(p.keys(), p.values(), p.descriptions()))

needs implementation of def descriptions:

[timosachsenberg]

probably needs more thinking