Change WXWIN example to make it more clear

[programmingkidx]

Currently in the build directions the WXWIN variable is set to a value that is probably not going to work for very many people. It is because it expects the wxWidgets folder to be located one folder above the current working directory.

I suggest this example be changed to this: export WXWIN=

This example makes it clear that the user is expected to supply their own path for the wxWidgets folder.

[mattip]

A PR would be nice