Missing documentation for User Defined Wind in InflowWind

[deslaughter]

Bug description

OpenFAST documentation hasn't been updated to explain how to use the user defined wind as part of the Flow Field code organization. This applies to main, dev, and dev-tc branches and needs to be fixed for the 4.2 release.

See thread at https://forums.nrel.gov/t/user-defined-windtype-in-inflowwind/9296 for relevant details.

[deslaughter]

Completed with #3225