update usage restrictions

docs/differentiation.md

@@ -13,7 +13,7 @@ The [adjoint differentiation mode](https://arxiv.org/abs/2009.02823) computes fi
 The Generalized parameter shift rule (GPSR mode) is an extension of the well known [parameter shift rule (PSR)](https://arxiv.org/abs/1811.11184) algorithm [to arbitrary quantum operations](https://arxiv.org/abs/2108.01218). Indeed, PSR only works for quantum operations whose generator has a single gap in its eigenvalue spectrum, GPSR extending to multi-gap.
 
 !!! warning "Usage restrictions"
-    At the moment, circuits with one or more Scale or HamiltonianEvolution operations are not supported.
+    At the moment, circuits with one or more Scale or HamiltonianEvolution with parametric generators operations are not supported.
     They should be handled differently as GPSR requires operations to be of the form presented below.
     Also, circuits with operations sharing a same parameter name are also not supported
     as such cases are handled by our other Python package for differentiable digital-analog quantum programs Qadence