[jitsi-dev] Addition to developer documentation

Hi,

The developer documentation describes how to set up the PATH environment
variable for your native libraries. This description is only valid for
Windows, since Linux uses a different environment variable.

Could you please add a bit of text that says that linux users should use
'LD_LIBRARY_PATH' instead?

Personally, I didn't know this and so I tried another setting for a
while which isn't completely without side effects I think.

Thanks,
Danny