improve docstring

Author: ufechner7

src/solver.jl

@@ -83,7 +83,7 @@ Main solving routine for the aerodynamic model. Reference point is in the kite b
 # Arguments:
 - solver::Solver: The solver to use, could be a VSM or LLT solver. See: [Solver](@ref)
 - body_aero::BodyAerodynamics: The aerodynamic body. See: [BodyAerodynamics](@ref)
-- gamma_distribution
+- gamma_distribution: Initial circulation vector or nothing; Length: Number of segments.
 
 # Keyword Arguments:
 - log=false: If true, print the number of iterations and other info.