chore: remove gunicorn and gevent from minimum requirements

It is now up to the user to install these (or other) for production deployment.
More info: https://flask.palletsprojects.com/en/1.1.x/tutorial/deploy/#run-with-a-production-server

docs/guide/installation.md

@@ -0,0 +1,34 @@
+---
+layout: default
+title: Basic installation
+nav_order: 2
+---
+
+
+Basic installation
+==================
+
+Download this repo and install the dependencies:
+
+```sh
+$ git clone https://github.com/lnbits/lnbits.git
+$ python3 -m venv .venv
+$ source ./.venv/bin/activate
+(.venv) $ pip install -r requirements.txt
+```
+
+You will need to set the variables in `.env.example`, and rename the file to `.env`.
+
+Run the migrations and the Flask server:
+
+```sh
+(.venv) $ flask migrate
+(.venv) $ flask run
+```
+
+You might also need to install additional packages, depending on the [backend wallet](./wallets.md) you use.
+E.g. when you want to use LND you have to run:
+
+```sh
+(.venv) $ pip install lnd-grpc
+```