Bug report: Typo in Structural Control (StC) Theory Documentation #2992

Bug description
As mentioned in the following forum topic: https://forums.nrel.gov/t/clarification-theoretical-background-of-tmd/9282, there is a typo in the Structural Control (StC) theory documentation and the subscript N/O_N should be used for the angular velocity terms of Eq. 4.217, as they are used earlier in the documentation.

The source code implementation is correct and this typo will not affect simulation results.

OpenFAST Version
Current main branch (OpenFAST v4.1.2)