Fix misleading documentation of `Topology.bonds` (#3968)

* Fix misleading documentation of `Topology.bonds`

`Topology.bonds()` states that iterates over a tuple of `Atom` objects. While this is technically correct, as the `Bond` class is a named tuple, this also hides the fact, that `Bond` objects also provide the `order` and `type` attributes. Therefore, I propose to change the sentence, so that it uses the capitalized *Bonds* indicating that they are actually objects.

* Update docstring

wrappers/python/openmm/app/topology.py

@@ -230,7 +230,9 @@ class Topology(object):
                     yield atom
 
     def bonds(self):
-        """Iterate over all bonds (each represented as a tuple of two Atoms) in the Topology."""
+        """Iterate over all bonds in the Topology.
+        Each one is represented by a Bond object, which is a named tuple of two atoms.
+        """
         return iter(self._bonds)
 
     def getPeriodicBoxVectors(self):