Update docs for FMSv2

[frankkopp]

BBK's findings:

• https://docs.flybywiresim.com/pilots-corner/advanced-guides/flight-planning/disco/#special-cases
  SID and En-route F-PLN Discontinuity - Inaccuracy
  -> No longer an issue

• STAR and Approach Discontinuity - Inaccuracy
  -> No longer an issue

• https://docs.flybywiresim.com/pilots-corner/a32nx-briefing/mcdu/f-pln/#general
  Missed Approach Procedure and ALTN Flight Plan
  -> Now implemented

• https://docs.flybywiresim.com/pilots-corner/a32nx-briefing/mcdu/f-pln/#lat-rev-page-elements

  • ENABLE ALTN (4L)
    -> Now implemented

• Unrelated: https://docs.flybywiresim.com/pilots-corner/a32nx-briefing/mcdu/f-pln/#vertical-revision-pages

  • TITLE:
    -> EFOB and EXTRA fuel are no longer shown IRL as of H3, so it's correct that we don't show it
  • ALT ERROR (4R):
    -> Was implemented with VNAV
  • CLB OR DES (6L, 6R)
    -> Was implemented a while back

• Unrelated: https://docs.flybywiresim.com/pilots-corner/a32nx-briefing/mcdu/f-pln/#constraints

  • "Currently not available or INOP in the FBW A32NX for Microsoft Flight Simulator."
    -> Speed and altitude constraints are implemented, only time constraints are not

[2hwk]

https://docs.flybywiresim.com/fbw-a32nx/feature-guides/cFMS/

also must be updated @BlueberryKing @Benjozork @Valastiri @frankkopp