document OpenSSL requirements on Windows

maybe it is a good idea to document what is necessary to have OpenSSL picked up by configure automatically on Windows:

1. download latest version from http://www.openssl.org/
2. set the following variables (assuming OpenSSL is installed in C:\OpenSSL):

• include path: "set include=%include%;C:\OpenSSL\include"
• path: "set path=%path%;C:\OpenSSL\bin"

Then configure will detect it automatically and enable run-time OpenSSL support, using QLibrary.

For linked OpenSSL support, you need to set the following:

• include path as above
• lib: set lib=%lib%;C:\OpenSSL\lib
• configure.exe -openssl-linked

Alternatively, one could also use the -I and -L switches in configure.exe; but I think for run-time support the dlls must be in the path also when running a program using SSL. For the linked-in support, using those switches should be fine.