Grammar installation instructions for Windows

[non-Jedi]

treesit-auto implicitly assumes the presence of a C compiler and linker on exec-path by relying on treesit-install-language-grammar for installing missing grammars. On linux this is a reasonable assumption, but it is rarely true on Windows. The grammar installation section of the README should either recommend either installing compiler tool-chain onto exec-path or directly downloading and manually installing the grammar. I'm not sure which is more preferable.

[ronisbr]

Hi @non-Jedi !

Since I do not have a Windows machine to test, I cannot help here unfortunately :(

[mzaffalon]

@non-Jedi Thank you for the clear instructions: I just tested and they work.

PR: #27 @non-Jedi Could you please review it?