module declaration example should always use claranet for readme

[xp-1000]

Currently, the modules readme generator script uses the current git reference as source.

we need to keep this because when someone use make init-stack command from its fork, the source should be correct to work with terraform init.

Nevertheless, this underlying script is also used to generated a fragment of the module readme and in this case this should always be claranet as source else the contribution from forks will never pass the CI.