document deprecation of playback <path> SDF param (#425)

Signed-off-by: Mabel Zhang <[email protected]>

Author: mabelzhang

Migration.md

@@ -32,6 +32,9 @@ Gazebo 2+ for playback. [BitBucket pull request
 #257](https://osrf-migration.github.io/ignition-gh-pages/#!/ignitionrobotics/ign-gazebo/pull-requests/257)
 added an SDF message to the start of log files.
 
+* Log playback using `<path>` SDF parameter is deprecated. Use `--playback`
+  command line argument instead.
+
 ## Ignition Gazebo 1.0.2 to 1.1.0
 
 * All headers in `gazebo/network` are no longer installed.

examples/worlds/log_playback.sdf

@@ -2,6 +2,9 @@
 <!--
   Log playback demo.
 
+  This file will be removed in Ignition Dome. Use the command line argument
+  for playback instead.
+
   Running this world will playback log files located at /tmp/log.
 
   You can record such a log by running one of the `log_record*.sdf` files,
@@ -15,6 +18,8 @@
     <plugin
       filename='libignition-gazebo-log-system.so'
       name='ignition::gazebo::systems::LogPlayback'>
+      <!-- Deprecation warning: This parameter will be removed in Ignition Dome.
+           Use the command line argument for playback instead. -->
       <path>/tmp/log</path>
     </plugin>
   </world>

tutorials/log.md

@@ -114,6 +114,9 @@ directory specified to record:
 
 ### From plugin in SDF
 
+This feature is deprecated and will be removed in Ignition Dome.
+Use the command line argument instead.
+
 Alternatively, playback can be specified in an SDF file. See example file
 `examples/worlds/log_playback.sdf`: