Update title of the hybrid PIC section to mention Ohm's law (BLAST-WarpX#6342)

Since the hybrid PIC model is documented as a field solver, I think it
makes sense to explicitly mention the field equation that it solves in
the title.

Author: RemiLehe

Docs/source/theory/kinetic_fluid_hybrid_model.rst

@@ -1,7 +1,7 @@
 .. _theory-kinetic-fluid-hybrid-model:
 
-Kinetic-fluid Hybrid Model
-==========================
+Maxwell-Ampere coupled with Ohm's law (a.k.a. "hybrid PIC")
+===========================================================
 
 Many problems in plasma physics fall in a class where both electron kinetics and electromagnetic waves do not
 play a critical role in the solution. Examples of such situations include the