Add custom converters to the docs

[rochacbruno]

The PR #784

allowed

# app.py
from pathlib import Path
from dynaconf.utils import parse_conf

parse_conf.converters["@path"] = (
    lambda value: value.set_casting(Path)
    if isinstance(value, parse_conf.Lazy)
    else Path(value)
)

# settings.toml

parent = "@path @format {env[HOME]}/parent"
child = "@path @format {this.parent}/child"

We need to add that to the docs and example/ test run

[jorenretel]

Hi,

I think I already added this: https://github.com/dynaconf/dynaconf/blob/master/example/custom_cast_token/app.py

That covers adding to example/ test run, right?

[rochacbruno]

sadly not @jorenretel , we want to automate those runs, but currently it runs via https://github.com/dynaconf/dynaconf/blob/master/Makefile#L9

[jorenretel]

I have put in a pull request: #791