Missing documentation for User Defined Wind in InflowWind

**Bug description**
<A clear and concise description of the bug.>

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.
