message: Add note about coefficient use cases
diff: @@ -30,7 +30,10 @@ class ParMesh;
  /** @brief Base class Coefficients that optionally depend on space and time.
  These are used by the BilinearFormIntegrator, LinearFormIntegrator, and
  NonlinearFormIntegrator classes to represent the physical coefficients in
  - the PDEs that are being discretized. */
  + the PDEs that are being discretized. This class can also be used in a more
  + general way to represent functions that don't necessarily belong to a FE
  + space, e.g., to project onto GridFunctions to use as initial conditions,
  + exact solutions, etc. See, e.g., ex4 or ex22 for these uses. */
  class Coefficient
  {
  protected:
  