GridCraft guides

1. 01How to install GridCraft on macOS, Windows and LinuxWhich GridCraft 0.5.0 file to download for your OS and CPU, how to verify it, and how to build GridCraft from source. Based on the official README and the v0.5.0 release.
2. 02GridCraft: a free, open-source Microsoft Excel alternativeWhat GridCraft 0.5.0 is, what it already does, and where it still falls short of Microsoft Excel. Based only on the official GridCraft README and docs.