Add 'help' function to ALMA

For displaying the valid inputs:
```
>>> Alma.help()
Valid ALMA keywords:

Position
  Source name (Sesame)             : source_name_sesame
  Source name (ALMA)               : source_name-asu
  RA Dec                           : raDecCoordinates

Energy
  Frequency                        : energy.frequency-asu
  Bandwidth                        : energy.bandwidth-asu
  Spectral resolution              : energy.resolution-asu
  Band                             : band-asu

Time
  Observation date                 : start_date-asu
  Integration time                 : int_time-asu

Polarisation
  Polarisation type                : energy.pol_num-asu

Observation
  Water vapour                     : pwv-asu

Project
  Project code                     : project_code-asu
  Project title                    : project.title-substr
  PI name                          : project.pi_name-substr

Options
  View:                            : viewFormat
  [x] public data only             : publicFilterFlag     = public
  [x] science observations only    : scan_intent-asu      = =%TARGET%
```