Seafile Apache2 config

I’d suggest adding ProxyPreserveHost to the Apache config examples in the docs, I found without it I was running into CRSF errors when trying to enable the 2FA (And in the case of safari I couldn’t even login without getting a CRSF error)

# seahub
#
SetEnvIf Authorization "(.*)" HTTP_AUTHORIZATION=$1
ProxyPass / http://127.0.0.1:8000/
ProxyPassReverse / http://127.0.0.1:8000/
ProxyPreserveHost ON

@daniel.pan

We will look into the problem.