Additional instructions for fmtk lsp setup in Neovim

[JohnTheCoolingFan]

Additional instructions for getting fmtk lsp to work with changelog and locale files in neovim, based on my experience.

Also added grammar parsing instructions and basic instructions on how to make highlight configuration for them.

For potential conflict with vim-polyglot's changelog filetype, I've filed an issue asking about how to avoid that: sheerun/vim-polyglot#857

I may update this in the future when I gather more information about the filetype setting conflict.

[JohnTheCoolingFan]

I've added additional filetype configuration so now in editor it would set the space indentation as default and convert tab usage to 2 spaces and use 2 spaces as indent steps. And also it would ignore changelog.txt fiels if there is no info.json in the same dir, narrowing down the match to Factorio mod project directories.