start updating recapitation vignette

doc/short_vignettes/recapitation.md

@@ -45,14 +45,26 @@ assert pop.generation == 10
 Now we use `msprime` to coalesce the founder generation roots back to a common ancestor:
 
 ```{code-cell} python
+import demes
 import msprime
 
+
 # Convert to tskit format
 ts = pop.dump_tables_to_tskit()
 
 num_roots_pre_recapitation = ts.first().num_roots
 
-recapitated_ts = msprime.simulate(from_ts=ts)
+yaml=f"""
+time_units: generations
+demes:
+ - name: deme0
+   epochs:
+    - start_size: {pop.N}
+"""
+graph = demes.loads(yaml)
+demography = msprime.Demography.from_demes(graph)
+
+recapitated_ts = msprime.sim_ancestry(demography=demography, initial_state=ts)
 
 print(num_roots_pre_recapitation, recapitated_ts.first().num_roots)
 ```