Hi. This is a great first question for the forum 
I agree that our documentation does not help much for complex synapse models like that. The complex part is not that it is a conductance-based synapse – the very simple models in the COBAHH example are conductance-based as well (that’s actually what “COBA” stands for). Here, the complexity rather stems from the fact that the synaptic conductance is a continuous function of the membrane potential, instead of being triggered by individual spikes. This can be useful in particular when analyzing models mathematically, but I personally would not recommend such models in most cases because they tend to be less efficient. As a minor inconvenience, also note that this model only works with (pre-synaptic) neuron models that model the action potential in detail, i.e. not with integrate-and-fire type models.
All that said, you can of course model this type of synapse with Brian. There are two broad approaches (s as part of the pre-synaptic neuron or s as part of the Synapses object), all depends on whether your time constants are the same across all synapses or whether they can vary between synapses. In your case I assume that they are supposed to be the same?