Clarify documentation on setEBDirchlet() and fix link to AMReX-Hydro (#3652)

## Summary

## Additional background

## Checklist

The proposed changes:
- [ ] fix a bug or incorrect behavior in AMReX
- [ ] add new capabilities to AMReX
- [ ] changes answers in the test suite to more than roundoff level
- [ ] are likely to significantly affect the results of downstream AMReX
users
- [ ] include documentation in the code and/or rst files, if appropriate

Author: cgilet

Docs/sphinx_documentation/source/LinearSolvers.rst

@@ -483,7 +483,9 @@ To set homogeneous Dirichlet boundary conditions, call
     ml_ebabeclap->setEBHomogDirichlet(lev, coeff);
 
 where coeff can be a real number (i.e. the value is the same at every cell)
-or is the MultiFab holding the coefficient of the gradient at each cell with an EB face.
+or a MultiFab holding the coefficient of the gradient at each cell with an EB face.
+In other words, coeff is :math:`\beta` in the canonical form given in equation :eq:`eqn::abeclap`
+located at the EB surface centroid.
 
 To set inhomogeneous Dirichlet boundary conditions, call
 
@@ -494,8 +496,9 @@ To set inhomogeneous Dirichlet boundary conditions, call
     ml_ebabeclap->setEBDirichlet(lev, phi_on_eb, coeff);
 
 where phi_on_eb is the MultiFab holding the Dirichlet values in every cut cell,
-and coeff again is a real number (i.e. the value is the same at every cell)
-or a MultiFab holding the coefficient of the gradient at each cell with an EB face.
+and coeff again is a real number
+or a MultiFab holding the coefficient of the gradient at each cell with an EB face,
+i.e. :math:`\beta` in equation :eq:`eqn::abeclap` located at the EB surface centroid.
 
 Currently there are options to define the face-based coefficients on
 face centers vs face centroids, and to interpret the solution variable

Docs/sphinx_documentation/source/conf.py

@@ -42,7 +42,7 @@ def get_amrex_version():
 
 intersphinx_mapping = {
     'amrex_tutorials': ('https://amrex-codes.github.io/amrex/tutorials_html/', None),
-    'amrex_hydro':('https://amrex-codes.github.io/amrex/hydro_html/', None)
+    'amrex_hydro':('https://amrex-fluids.github.io/amrex-hydro/docs_html/', None)
 }
 
 # Add any paths that contain templates here, relative to this directory.