Fix install instructions by specifying branch

[marcs-feh]

When the branch is not specified in the install info neovim will guess it is master, however this repo uses main which causes a mv command to fail during install, to fix, simply specify that in the install_info

local parser_confs = require 'nvim-treesitter.parsers'.get_parser_configs()
parser_confs.odin = {
    install_info = {
        url = 'https://github.com/ap29600/tree-sitter-odin',
        branch = 'main',
        files = {"src/parser.c"}
  },
    filetype = "odin",
}