Add command to print the enstrophy of the initial condition

README.md

@@ -58,7 +58,14 @@ The available commands are
 
 * `uk`: to compute the Fourier transform of the solution.
 
-* `quiet`: does not print anything, useful for debugging.
+* `quiet`: does not print anything (useful for debugging).
+
+* `enstrophy_print_init`: to compute the enstrophy and various other
+  observables for the initial condition (useful for debugging). The command
+  prints
+  ```
+  alpha energy enstrophy
+  ```
 
 
 # Parameters