nvim: init: Always enable the signcolumn

Have a fixed column for the diagnostics to appear in as this removes
the jitter when warnings/errors flow in.

Recommended here
https://sharksforarms.dev/posts/neovim-rust/

nvim/.config/nvim/init.lua

@@ -45,6 +45,7 @@ vim.o.diffopt        = 'filler,internal,algorithm:histogram,indent-heuristic'
 vim.o.scrolloff      = 999
 vim.o.formatoptions  = "crqn1j"
 vim.o.relativenumber = true
+vim.o.signcolumn     = "yes"
 
 vim.g.python3_host_prog       = '/usr/bin/python3'
 -- Disable providers we do not give a shit about