Update the documentation reference (#1361)

### Summary
PR #248 moved the location of `drift-detect.md`. This PR adjusts source
to point to: https://lyft.github.io/cartography/usage/drift-detect.html

### Related issues or links


### Checklist

Provide proof that this works (this makes reviews move faster). Please
perform one or more of the following:
- [ ] Update/add unit or integration tests.
- [ ] Include a screenshot showing what the graph looked like before and
after your changes.
- [ ] Include console log trace showing what happened before and after
your changes.

If you are changing a node or relationship:
- [ ] Update the
[schema](https://github.com/lyft/cartography/tree/master/docs/root/modules)
and
[readme](https://github.com/lyft/cartography/blob/master/docs/schema/README.md).

If you are implementing a new intel module:
- [ ] Use the NodeSchema [data
model](https://lyft.github.io/cartography/dev/writing-intel-modules.html#defining-a-node).

---------

Signed-off-by: Emmanuel Ferdman <emmanuelferdman@gmail.com>

cartography/driftdetect/cli.py

@@ -30,7 +30,7 @@ def _build_parser(self):
                 'graph database and reports the deviations.'
             ),
             epilog='For more documentation please visit: '
-                   'https://github.com/lyft/cartography/blob/master/docs/drift-detect.md',
+                   'https://lyft.github.io/cartography/usage/drift-detect.html',
         )
         parser.add_argument(
             '-v',