add comment about Connext security plugins not being included in dock…

…er images

Signed-off-by: Mikael Arguedas <mikael.arguedas@gmail.com>

.github/workflows/test.yml

@@ -9,6 +9,8 @@ on:
 jobs:
   test_latest:
     runs-on: ubuntu-latest
+    # 'osrf/ros2:devel' does *not* include RTI Connext or its' security plugins
+    # the former gets installed via rosdep in 'action-ros-ci' but the latter do *not* get installed
     container: osrf/ros2:devel
     steps:
     - name: Install prerequisites for action-ros-ci and FastRTPS
@@ -42,6 +44,8 @@ jobs:
         path: ros_ws/log
   test_nightly:
     runs-on: ubuntu-latest
+    # 'osrf/ros2:nightly-rmw-nonfree' includes RTI Connext but
+    # does *not* include the security plugins or a license allowing the use of Security
     container: osrf/ros2:nightly-rmw-nonfree
     steps:
     - uses: actions/checkout@v2