Add updating documentation

closes #4036

docs/updating.md

@@ -0,0 +1,31 @@
+# How to update
+
+To update your freqtrade installation, please use one of the below methods, corresponding to your installation method.
+
+## docker-compose
+
+!!! Note "Legacy installations using the `master` image"
+    We're switching from master to stable for the release Images - please adjust your docker-file and replace `freqtradeorg/freqtrade:master` with `freqtradeorg/freqtrade:stable`
+
+``` bash
+docker-compose pull
+docker-compose up -d
+```
+
+## Installation via setup script
+
+``` bash
+./setup.sh --update
+```
+
+!!! Note
+    Make sure to run this command with your virtual environment disabled!
+
+## Plain native installation
+
+Please ensure that you're also updating dependencies - otherwise things might break without you noticing.
+
+``` bash
+git pull
+pip install -U -r requirements.txt
+```

mkdocs.yml

@@ -31,6 +31,7 @@ nav:
     - Advanced Strategy: strategy-advanced.md
     - Advanced Hyperopt: advanced-hyperopt.md
     - Sandbox Testing: sandbox-testing.md
+    - Updating Freqtrade: updating.md
     - Deprecated Features: deprecated.md
     - Contributors Guide: developer.md
 theme: