Provide instructions for Windows systems

[matteosecli]

This doesn't mean that there is an official Windows support; prebuilt packages (with e.g. Cygwin, GS and Java) will not be provided (as I don't have a chance to test them, so it's pointless so ship something untested).

However, being GS and Java cross-platform, there should be in principle no obstacle in running pdf2archive in Windows (once one has a Bash shell). Additionally, given that I've put up pdf2archive right because Linux is discriminated in the availability of free PDF/A-1B converting solutions, it would not be nice to "discriminate back" Windows.

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Possible solutions

• For Windows 10 on
  An option would be to use the WSL. Checks are needed.
• For older versions
  I think we need something like Cygwin. Users can be instructed to open a Cygwin terminal and run pdf2archive as you would do on Linux, or we can provide them with a .bat wrapper. Checks are needed.

TODO

• Find someone willing to test on Windows, as I don't have a Windows box available (and I don't plan to have one).
• Test the solution with WSL on Windows 10.
• Test the solution with Cygwin, both with and without a .bat.
• Provide instructions for installing Ghostscript, Java and a WSL Linux distro (or Cygwin).