Document that recordings can only be made from NeuroML segment mid-points

[sanjayankur31]

since these are the points at which jLEMS simulates the model. So, one can find the various segments and mention which to record from, and the recording will be made from its midpoint. These are seamlessly converted to NEURON section co-ordinates, but it may not always be possible to record from soma.v(0.5) as in NEURON.

Should go on the paths/recordings page perhaps.