README: Add clean and ccache instructions

README.md

@@ -126,6 +126,25 @@ A new `tmp_build_dir` directory will be created to store the compiled object and
 auxiliary files. Assuming all is well, you should have an executable in the
 current directory of the form `main<config>.ex` e.g. `main3d.gnu.MPI.OMP.ex`.
 
+If you want to clean the current build configuration you can do
+```bash
+make cleanconfig
+```
+Note that this is similar to `make clean` for GRChombo examples.
+
+If you want to clean all build configuration, you can do
+```bash
+make clean
+```
+Note that this is similar to `make realclean` for GRChombo examples.
+
+To speed up subsequent compilations, you can install
+[Ccache](https://ccache.dev/) and then add
+```
+USE_CCACHE = TRUE
+```
+to your `Make.local-pre` configuration file.
+
 ## Running the code
 
 You can run the example as for GRChombo by passing the parameter file as the