dependencies are incomplete, extra helper commands

in Ubuntu 22.04, `apt install ...`
 - python3.10-venv
 - gcc
 
Proxy requirement for treesitter:
```
HTTP_PROXY= ...
HTTPS_PROXY=..
```

Packer install command fails, requires multiple runs inside nvim

Add nvim unstable ppa:
https://launchpad.net/~neovim-ppa/+archive/ubuntu/unstable

update alternatives:
```
sudo update-alternatives --config vim
```