docstrings for edi.py

Signed-off-by: LK <LK@uni>
docstrings for z.py

Signed-off-by: LK <LK@uni>
docstrings for z.py

Signed-off-by: LK <LK@uni>
extended readme

Signed-off-by: LK <LK@uni>
changed Edi.py to km/s as standard unit for Z

Signed-off-by: LK <LK@uni>
changed Z.py to km/s as standard unit for Z

Signed-off-by: LK <LK@uni>
added read-methods to the PhaseTensor class in pt.py

Signed-off-by: LK <LK@uni>