a_howto_calculation_point_distance

[Jonasvsl]

• should have an illustration to show how calculation point distance works.
• "40 x 40 m^2" should use math expression
• Needs a link to concepts where is explained what double connectec, connected, embedded etc is (h_1d2d_exchange.rst)
• "Pipes can also be given a connected calculation type, in combination with a calculation point distance that is smaller than the length of the pipe. In this way, the pipe can exchange with 2D cells it crosses. This can be used as a way to schematise gullies." This also needs an illustraion

[JohannaLems]

the illustration to show how calculation point distance works, already exists: https://docs.3di.live/h_computational_grid.html#calculation-point-distance & https://docs.3di.live/h_onedee_flow.html#channels-culverts-and-pipes