document columns of as.data.table(po())

[mb706]

• document what the columns mean
• short documentation of the types in the type columns
  • 'NULL', null object, but means no data, e.g. output of learner during train
  • '*' means any type, e.g. pipeopnop, pipeopcopy
  • [ ] means multiplicity, link to multiplicity
• input number columns: document 'NA' means number depends on construction argument.

[mb706]

(also document other columns I dont mention here obvs)