Rollback documentation and code inconsistency

There is a sentence in the transactions' documentation:
> If a commit() transactions fails, it should be terminated manually with rollback() after catching the failure.

And there is a code of `commit()` implementation:
```
try {
if (this.hasModifications()) {
this.graph.commit(this.addedRelations.getAll(), this.deletedRelations.values(), this);
} else {
this.txHandle.commit();
}

success = true;
} catch (Exception var9) {
try {
this.txHandle.rollback();
} catch (BackendException var8) {
throw new JanusGraphException("Could not rollback after a failed commit", var9);
}

throw new JanusGraphException("Could not commit transaction due to exception during persistence", var9);
}
```
As I see here, the `rollback()` is called if `commit()` is failed.
I think that the documentation should say:
`If a commit() transactions fails, it will be terminated automatically with rollback()`
or something like that. Maybe some clarification should be put there.

Start with the transactions documentation sentence and the commit() implementation shown in the issue. Confirm the documented behavior against the implementation, then revise the transaction guidance so it accurately describes failure handling; it is done when the documentation is consistent and clear.

Written by the indexing model from the issue text.