Update to version 0.2.0 in the documentation

The current user documentation is aligned to the latest
changes in the API client, and not to the previous version.

Signed-off-by: Daniel Zullo <daniel.zullo@frequenz.com>

README.md

@@ -30,7 +30,7 @@ You can install the Frequenz Electricity Trading API client via pip. Replace `VE
 
 ```
 # Choose the version you want to install
-VERSION=0.1.0
+VERSION=0.2.0
 pip install frequenz-client-electricity-trading==$VERSION
 ```