Update basic-csharp-mod.md (Correcting misleading instructions)

[leesugil]

In the Setting up your Project section, there are a couple of slightly misleading instructions that are not entirely true, causing extra pain points to readers wishing to join the modding community.

At step 5, it says to refer all Taleworld.*.dll files to your C# project in Visual Studio, but Taleworlds.Native.dll is not written in C# and therefore shows up an error message when readers try to follow the instruction.

At step 6, the same situation happens when readers follow the instruction for the Multiplayer module.

These two are clearly misleading causing extra pain points to new readers ("it doesn't work in my PC").

This commit clarifies these misleading "do this to all, every" instructions by stating that not all files will be referenced properly, therefore the current error messages are normal.