Change an to a

docs/sources/use/port_redirection.rst

@@ -31,7 +31,7 @@ container, Docker provide ways to bind the container port to an
 interface of the host system. To simplify communication between
 containers, Docker provides the linking mechanism.
 
-Binding a port to an host interface
+Binding a port to a host interface
 -----------------------------------
 
 To bind a port of the container to a specific interface of the host