feat: add submodule for soft-era-nvim

[gilmoregrills]

Hiiii 👋

Hope this is ok but I was trying to get the vim version of the theme working on neovim and it wasn't working, so I sorta just made a neovim version with lush that's compatible with lualine/telescope/etc.

Idk if you fancy including it here but I thought I'd create a PR to add it just in case you did.

Thanks!