Windows from-sauce instructions aren't exact

[zoffixznet]

1. The prerequisites section should list the need for a .tar.gz archive unpacker, like 7-zip
2. The unpacking step should mention that 7-zip requires two stages of unpacking, because first it only unpacks the .gz portion, leaving the user with just the .tar file, which also needs to be unpacked before the rest of the instructions can be executed.
3. The shown command to run after unpacking is cd C:\Temp\rakudo-star yet, the unpacked star dir has a version number in it
4. During installation (possibly during spectest) firewall warning comes up (RT#130358). It's a bit scary-looking when totally unexpected, so might be nice to mention its possibility in the install guide.

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It's also a bit convoluted: Chrome downloaded the file into my Downloads folder and I unpacked the stuff there, but now—per instructions—I need to figure out how to move that directory to \Temp. Would running the build in Downloads dir work? Would it still work in dirs that have spaces in them?