Add the documentation how to configure Kutt (#368)

* Add a the documentation how to configure Kutt

* Added link to official docker hub image

* Fix typo

README.md

@@ -60,20 +60,33 @@ If you're coming from v1, refer to [MIGRATION.md](MIGRATION.md) to migrate data
 
 ## Setup
 
+### Manual
+
 You need to have [Node.js](https://nodejs.org/), [PostgreSQL](https://www.postgresql.org/) and [Redis](https://redis.io/) installed.
 
-1. Clone this repository or [download zip](https://github.com/thedevs-network/kutt/archive/v2-beta.zip).
-2. Copy `.example.env` to `.env` and fill it properly.
+1. Clone this repository or [download the latest zip](https://github.com/thedevs-network/kutt/releases).
+2. Copy `.example.env` to `.env` and fill it properly ([see below](#configuration)).
 3. Install dependencies: `npm install`.
 4. Run for development: `npm run dev`.
 5. Run for production: `npm run build` then `npm start`.
 
 ### Docker
 
-You need to run the app with the required envrironment variables listed in [.example.env](https://github.com/thedevs-network/kutt/blob/develop/.example.env). 
+Download the `docker-compose.yml` and the `.docker.env`-file from the repository and configure the `.docker.env` ([see below](#configuration)). 
+To execute Kutt you simply have to run `docker-compose up -d` command and then the app should be ready on port "3000".
+
+The `docker-compose.yml` uses the official kutt docker image available on [Docker Hub](https://hub.docker.com/r/kutt/kutt).
+
+### Configuration
+
+For the minimal configuration the following settings have to be changed in the `.env`-file:
 
-* [Official Docker hub image](https://hub.docker.com/r/kutt/kutt). 
-* Or simply run `docker-compose up` command and then the app should be ready on port "3000".
+- **DEFAULT_DOMAIN**: The domain of your kutt instance
+- **DB_**: The DB credentials (when you use docker-compose you can skip these)
+- **ADMIN_EMAILS**: A comma-separated list of the administrator-accounts
+- **RECAPTCHA_**: Enter your credentials to use reCaptchas or delete this setting if you don't want to use it
+- **MAIL_**: Enter the SMTP-server's credentials (The experience shows SSL works better than STARTTLS; The mail config is required to easily create accounts, see [this comment](https://github.com/thedevs-network/kutt/issues/269#issuecomment-628604256) how it can be done manually)
+- **REPORT_EMAIL**: Kutt offers a form to report malicious links which are sent to this mail-address
 
 ## Browser Extensions