Would be good to indicate that kommentary requires NeoVim 0.5+

[andrewferrier]

Starting kommentary with Neovim < 0.5 gives an error:

line    3:
E5105: Error while calling lua chunk: ...pack/packager/start/kommentary/lua/kommentary/config.lua:121: attempt to index field 'g' (a nil value)

It works fine in 0.5+.

I guess this is probably to be expected, but it might be good to note that 0.5 is the minimum required version in the README.

Thanks for your hard work on this great plugin!