Fix language tag and make example pasteable in README.md

README.md

@@ -75,10 +75,12 @@ translate these docs to Python code.
 Python does not allow `!` in function names, so this is also [a limitation of pyjulia](https://pyjulia.readthedocs.io/en/latest/limitations.html#mismatch-in-valid-set-of-identifiers)
 To use functions which on the Julia side have a `!`, like `step!`, replace `!` by `_b`, for example:
 
-```julia
+```py
 from diffeqpy import de
+
 def f(u,p,t):
     return -u
+
 u0 = 0.5
 tspan = (0., 1.)
 prob = de.ODEProblem(f, u0, tspan)