Documentation site for 2.0-alpha1

[tdviet]

The documentation of the 2,0-alpha1 version is available at

https://fedcloudclient.readthedocs.io/en/2.0-alpha1/

for easy reading and improvement.

Once 2.0 version is released, the main docs site https://fedcloudclient.fedcloud.eu/ will be updated to enable showing multiple versions