Label axis on pandas group by plot

Question

I'm plotting a pandas dataframe with structure similar to

index groupcol value
1    A          10
2    B          12
3    C          10
4    A          10
5    C          17
6    A          11
7    B          15

with

df.groupby([df.index,'groupcol']).mean()['value'].unstack().plot(subplots=True, layout=(3,1))

So I get a row of three graphs. How can I add a general x and y labels to the entire plot and not to the individual graphs?