Document the initial config file

[sayanarijit]

We definitely could use some docs in https://github.com/sayanarijit/xplr/blob/main/src/init.lua.

[sayanarijit]

It will take a lot of effort maintaining different docs, both in the default init.lua and in https://xplr.dev/en/general-config.

So, let's look into a way to auto generate config from Lua file.

[sayanarijit]

Documented the general config in init.lua. Let's finish it and auto generate api docs from it.