README: disabling luarocks integration with README way does not work

[matu3ba]

See natecraddock/telescope-zf-native.nvim#21

There appear to be multiple ways to disable luarocks integration and plugins adding rockspec may be breaking with the information in the README

require('lazy').setup('my_plugins', { rocks = { enabled = false } })

works for me, but

require('lazy').setup('my_plugins', { pkg = { sources = "" } })

does not and fails with "build needed".

README may give a hint, but should not give incorrect/non-working information.

[folke]

The docs clearly state: You can remove rockspec from opts.pkg.sources to disable this feature.
It does not tell you to set it to ""