Add import statement for obstore in examples

[jbusecke]

Just ran into an issue with the example here. I think we might also be able to replace

obstore.get(store, filename) 
# with
store.get(filename)

?

[kylebarron]

I intended to switch all the examples to use class methods instead of pure functions but I know I've missed a few

[kylebarron]

Would you be able to instead fix this example by switching to store.get?