Seperate requirements to run the bot and to develop.

- Add a requirements-dev.txt file which includes additional deps for development.
- Add a Dockerfile.develop which installs all deps for development and also enables dev commands.
- Change related documentations on how to run/dev the bot.

docs/installation.md

@@ -134,6 +134,13 @@ cd freqtrade
 docker build -t freqtrade .
 ```
 
+If you are developing using Docker, use `Dockerfile.develop` instead, which will also set up develop dependencies:
+
+```bash
+cd freqtrade
+docker build -f ./Dockerfile.develop -t freqtrade .
+```
+
 For security reasons, your configuration file will not be included in the image, you will need to bind mount it. It is also advised to bind mount an SQLite database file (see the "5. Run a restartable docker image" section) to keep it between  updates.
 
 ### 3. Verify the Docker image