Fixes the pose graph example documentation.

Change-Id: Ia20f1463c042785bdae32568de77750d41963c3c

examples/slam/pose_graph_2d/README.md

diff --git a/examples/slam/pose_graph_2d/README.md b/examples/slam/pose_graph_2d/README.md
index fed51a6..b5ff987 100644
--- a/examples/slam/pose_graph_2d/README.md
+++ b/examples/slam/pose_graph_2d/README.md
@@ -33,11 +33,11 @@
 where `pose_id` is the corresponding integer ID from the file definition. Note,
 the file will be sorted in ascending order for the `pose_id`.
 
-The executable `pose_graph_2d` expects the first argument to be the path to the
+The executable `pose_graph_2d` has one flag `--input` which is the path to the
 problem definition. To run the executable,
 
 ```
-/path/to/bin/pose_graph_2d /path/to/dataset/dataset.g2o
+/path/to/bin/pose_graph_2d --input /path/to/dataset/dataset.g2o
 ```
 
 A python script is provided to visualize the resulting output files.

examples/slam/pose_graph_3d/README.md

diff --git a/examples/slam/pose_graph_3d/README.md b/examples/slam/pose_graph_3d/README.md
index a16aa09..badc1ec 100644
--- a/examples/slam/pose_graph_3d/README.md
+++ b/examples/slam/pose_graph_3d/README.md
@@ -39,12 +39,12 @@
 ...
 ```
 where `pose_id` is the corresponding integer ID from the file definition. Note,
-the file will be sorted in ascending order for the ```pose_id```.
+the file will be sorted in ascending order for the `pose_id`.
 
-The executable `pose_graph_3d` expects the first argument to be the path to the
+The executable `pose_graph_3d` has one flag `--input` which is the path to the
 problem definition. To run the executable,
 ```
-/path/to/bin/pose_graph_3d /path/to/dataset/dataset.g2o
+/path/to/bin/pose_graph_3d --input /path/to/dataset/dataset.g2o
 ```
 
 A script is provided to visualize the resulting output files. There is also an