Update README with git subtrees

Author: roschaefer

README.md

@@ -1,12 +1,27 @@
 # human-connection-api-nodejs-client
 [![Build Status](https://travis-ci.org/roschaefer/human-connection-api-nodejs-client.svg?branch=master)](https://travis-ci.org/roschaefer/human-connection-api-nodejs-client)
 
-Have a local Human Connection API server running on [port 3030](http:://localhost:3030), see [instructions](https://github.com/Human-Connection/API).
+## Prerequisites
+The development environment of this plugin uses the backend APIs of [Human Connection](https://human-connection.org/) and [Democracy](https://www.democracy-deutschland.de/#!start).
+If you clone this repository, you have a version of both backend APIs in [/democracy-server](/democracy-server) and [/human-connection-api](/human-connection-api) as [git subtrees](https://git-scm.com/book/en/v1/Git-Tools-Subtree-Merging), respectively.
+Follow the installation instructions of both Human Connection API and Democracy API:
+
+https://github.com/demokratie-live/democracy-server
+https://github.com/Human-Connection/API
+
+
+## Installation
+
+Install dependencies with [yarn](https://yarnpkg.com/en/):
+```sh
+yarn install
+```
+
+## Run
 
 Make sure you have [node](https://nodejs.org/en/) installed with a version >= 9.0.0.
 
 Then run:
-
 ```sh
 node --experimental-modules index.mjs
 
@@ -16,4 +31,3 @@ Or
 ```sh
 yarn start
 ```
-if you have yarn installed.