Add Polish translation

[VerticalHeretic]

This feature request was motivated by talks on Discord docs channel and copies flow shown in PR like #807 or #751. So this issue is for organization reasons and to document the progress:

Index

File	Status	Progress	Editor
index.md	Done	100%	@VerticalHeretic

Install

File	Status	Progress	Editor
linux.md	Done	100%	@VerticalHeretic
macos.md	Done	100%	@VerticalHeretic

Getting Started

File	Status	Progress	Editor
hello-world.md	Done	100%	@VerticalHeretic
folder-structure.md	Done	100%	@VerticalHeretic
spm.md	Done	100%	@VerticalHeretic
xcode.md	Done	100%	@VerticalHeretic

Basic

File	Status	Progress	Editor
routing.md	In Progress	100%	@VerticalHeretic
content.md	In Progress	0%	@VerticalHeretic
client.md	Open
validation.md	Open
async.md	Open
logging.md	Open
environment.md	Open
errors.md	Open
controllers.md	Open

Fluent

File	Status	Progress	Editor
overview.md	Open
model.md	Open
relations.md	Open
migration.md	Open
query.md	Open
transaction.md	Open
schema.md	Open
advanced.md	Open

Leaf

File	Status	Progress	Editor
getting-started.md	Open
overview.md	Open
custom-tags.md	Open

Redis

File	Status	Progress	Editor
overview.md	Open
sessions.md	Open

Advanced

File	Status	Progress	Editor
middleware.md	Open
testing.md	Open
server.md	Open
files.md	Open
commands.md	Open
queues.md	Open
websockets.md	Open
sessions.md	Open
services.md	Open
apns.md	Open

Security

File	Status	Progress	Editor
authentication.md	Open
crypto.md	Open
passwords.md	Open
jwt.md	Open

Deploy

File	Status	Progress	Editor
digital-ocean.md	Open
heroku.md	Open
supervisor.md	Open
systemd.md	Open
ngix.md	Open
docker.md	Open

Contributing

File	Status	Progress	Editor
contributing.md	Open

Version (4.0)

File	Status	Progress	Editor
legacy-docs.md	Open
upgrading.md	Open

Release Notes

File	Status	Progress	Editor
release-notes.md	Open