Document support for Destructure.XXX() methods and XXX.With<T>() methods

[tsimbalar]

Once #20 is implemented in the core repo, remember to update the documentation here !

See :

• Add support from .Destructure.XXX() methods and extension methods in ReadFrom.KeyValuePairSettings serilog#1172
• Add support for .Destructure.AsScalar(Type scalarType) method in KeyValuePairSettings serilog#1177
• Settings: Allow to disambiguate different calls to same method resulting in same key serilog#1178