Added info on ports.

docs/developer-guide.md

-# Aura Engine Development Guide
+# 1. Aura Engine Development Guide
 
 This page gives insights on extending Aura Engine internals or through the API.
 
+<!-- TOC -->
 
-## Architecture
+- [1. Aura Engine Development Guide](#1-aura-engine-development-guide)
+    - [1.1. Architecture](#11-architecture)
+    - [1.2. Required Data Sources](#12-required-data-sources)
+    - [1.3. Provided API Endpoints](#13-provided-api-endpoints)
+    - [1.4. Components](#14-components)
+    - [1.5. Running the Engine](#15-running-the-engine)
+    - [1.6. Default ports used by Engine](#16-default-ports-used-by-engine)
+
+<!-- /TOC -->
+
+## 1.1. Architecture
 
 AURA Engine as part of the AURA Radio Suite uses an modulear architecture
 based on a REST API. All external information is retrieved using JSON data-structures.
 
 To get the basic architectural overview, visit the [Aura Meta](https://gitlab.servus.at/autoradio/meta) repository.
 
-## Required Data Sources
+## 1.2. Required Data Sources
 
 The AURA Project "**Dashboard**" provides the GUI to organize shows, schedules/timelsots
 and organize uploads in form of playlists. Those playlists can be organized in timeslots
@@ -34,7 +45,7 @@ to be played and its meta-data:
 More information you can find here: <https://gitlab.servus.at/autoradio/meta/blob/master/api-definition.md>
 
 
-## Provided API Endpoints
+## 1.3. Provided API Endpoints
 
 **Soundserverstate:** Returns true and false values of the internal In- and Outputs  
 
@@ -46,7 +57,7 @@ More information you can find here: <https://gitlab.servus.at/autoradio/meta/blo
 /api/v1/trackservice/
 
 
-## Components
+## 1.4. Components
 
 
 **aura.py**: It is the server which is connected to the external programme source (e.g. aura steering and tank), to liquidsoap and is listening for redis pubsub messages. This precious little server is telling liquidsoap what to play and when.
@@ -56,7 +67,7 @@ More information you can find here: <https://gitlab.servus.at/autoradio/meta/blo
 **Liquidsoap**: The heart of AuRa Engine. It uses the built in mixer, to switch between different sources. It records everything and streams everything depending on your settings in aura.ini.
 
 
-## Running the Engine
+## 1.5. Running the Engine
 
 Aura Engine is consisting of two components: The Python Engine and Liquidsoap Core.
 
@@ -69,3 +80,14 @@ It's important to start both components in the correct order:
     2. Run the Liquidsoap core
 
     ./run.sh lqs
+
+
+## 1.6. Default ports used by Engine
+
+Aura Engine requires a number of ports for internal and external communication.
+
+Those are the default port numbers:
+
+* `1234` ... Liquidsoap Telnet Server
+* `3333` ... Exposes the Engine API
+* `5000` ... Svelte development mode; dynamically uses some other port if occupied