Update FGFunction documentation #116

Job	Run time
MSIS code validation (ubuntu-latest)	7s
MSIS code validation (macos-latest)	7s
XML validation	23s
C/C++ build (MSVC) (ON)	6m 43s
C/C++ build (Linux) (ubuntu-22.04, ON, ON, OFF, ON)	3m 48s
C/C++ build (MSVC) (OFF)	4m 37s
C/C++ build (MacOSX) (macos-12, 3.8)	5m 27s
C/C++ build (MinGW) (ON)	3m 21s
C/C++ build (Linux) (ubuntu-22.04, ON, OFF, OFF, ON)	3m 55s
C/C++ build (MacOSX) (macos-14, 3.10)	2m 14s
C/C++ build (MinGW) (OFF)	3m 57s
C/C++ build (Linux) (ubuntu-22.04, OFF, ON, OFF, ON)	3m 37s
C/C++ build (Linux) (ubuntu-22.04, OFF, OFF, OFF, ON)	3m 54s
C/C++ build (Linux) (ubuntu-20.04, OFF, OFF, ON, OFF)	5m 18s
Code coverage	1m 50s
Build Python Module from Source	0s
Matlab S-Function (macos-12)	5m 29s
Matlab S-Function (ubuntu-22.04)	2m 37s
Build Python wheels	0s
Matlab S-Function (windows-latest)	6m 10s
Build Windows installer	0s
Deploy Rolling Release	0s
Deploy Stable Release	0s
Deploy Documentation	0s
	1h 3m 34s

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