Add discussion in user's guide on depletion caveats
Add discussion in user's guide on depletion caveats

Potential over-depletion using the fission-q
energy deposition mode and some remedies.

Repeated burnable materials are depleted as a single material
unless diff_burnable_mats=True is given to the Operator

shikhar413/openmc,liangjg/openmc,liangjg/openmc,mit-crpg/openmc,amandalund/openmc,smharper/openmc,paulromano/openmc,mit-crpg/openmc,smharper/openmc,walshjon/openmc,liangjg/openmc,amandalund/openmc,paulromano/openmc,paulromano/openmc,shikhar413/openmc,mit-crpg/openmc,shikhar413/openmc,walshjon/openmc,amandalund/openmc,paulromano/openmc,mit-crpg/openmc,walshjon/openmc,smharper/openmc,liangjg/openmc,amandalund/openmc,smharper/openmc,walshjon/openmc,shikhar413/openmc