Update README.md

Add backticks so that file names and variables are rendered correctly.

README.md

@@ -12,21 +12,21 @@ When adding a new Riemann solver, in addition to adding the normal and
 (optionally) transverse solver code files in src/, you should do the following
 in order to ensure the new solver is importable in PyClaw.  To make things
 concrete, suppose you are committing a 2D elasticity solver, so your Fortran 
-files are named rpn2_elasticity.f90 and rpt2_elasticity.f90.  Then you should:
+files are named `rpn2_elasticity.f90` and `rpt2_elasticity.f90`.  Then you should:
 
-1. Add the following to clawpack/riemann/riemann/__init__.py:
+1. Add the following to `clawpack/riemann/riemann/__init__.py`:
 ```
 import vc_elasticity_2D
 ```
-2. Add 'vc_elasticity' to two_d_riemann in clawpack/riemann/riemann/setup.py.
-3. Add appropriate entries for num_eqn and num_waves in clawpack/riemann/riemann/static.py.
+2. Add `vc_elasticity` to `two_d_riemann` in `clawpack/riemann/riemann/setup.py`.
+3. Add appropriate entries for `num_eqn` and `num_waves` in `clawpack/riemann/riemann/static.py`.
 
-If you are adding a Python solver, then you should have a vc_elasticity_2D_py.py 
-file in clawpack/riemann/riemann. Assuming it contains a function vc_elasticity_2D, then 
+If you are adding a Python solver, then you should have a `vc_elasticity_2D_py.py` 
+file in `clawpack/riemann/riemann`. Assuming it contains a function `vc_elasticity_2D`, then 
 you should do:
 
-1. Add the following to clawpack/riemann/riemann/__init__.py:
+1. Add the following to `clawpack/riemann/riemann/__init__.py`:
 ```
 from vc_elasticity_2D_py import vc_elasticity_2D
 ```
-2. Add appropriate entries for num_eqn and num_waves in clawpack/riemann/riemann/static.py.
+2. Add appropriate entries for `num_eqn` and `num_waves` in `clawpack/riemann/riemann/static.py`.