Add a label to make it easier to download the latest/stable version

[LittleNewton]

neovim's release page has a lot of tags like v0.10.2, and also two special meta-tags:

• nightly
• stable

These two meta-tags make it easier to pull the latest version of neovim. The latest stable version of neovim can be pulled easily:

curl -LO https://github.com/neovim/neovim/releases/download/stable/nvim.appimage

Could you please add those tags to this repo?