Update installation command for HDF5 support

pip install now throws "WARNING: pandablocks 0.10.4 does not provide the extra 'hdf5'"

Author: tomtrafford

docs/tutorials/installation.md

@@ -30,7 +30,7 @@ $ python3 -m pip install pandablocks
 If you need to write HDF files you should install the hdf5 extra:
 
 ```
-$ python3 -m pip install pandablocks[hdf5]
+$ python3 -m pip install pandablocks[h5py]
 ```
 
 If you require a feature that is not currently released you can also install