Developer docs: Add note about symlink issue
Developer docs: Add note about symlink issue

If people see the test failures described in the node,
it is because they need to  restart VirtualBox as
described in this comment:

https://www.virtualbox.org/ticket/10085#comment:28

heartsucker/securedrop,garrettr/securedrop,garrettr/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,conorsch/securedrop,garrettr/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,conorsch/securedrop,garrettr/securedrop,ehartsuyker/securedrop,heartsucker/securedrop,conorsch/securedrop,micahflee/securedrop,micahflee/securedrop,micahflee/securedrop,heartsucker/securedrop,conorsch/securedrop,conorsch/securedrop,micahflee/securedrop