Add build map docs

[708yamaguchi]

Update README about building a map with Fetch robot.
Duplicate of knorth55#139

[k-okada]

this PR includes fetch.launch, but could not find code to include '($find jsk_fetch_startup)/launch/fetch.launch'

[knorth55]

fetch.launch is added for melodic update and not merged yet to jsk-ros-pkg/jsk_robot:master.
#1316
#1328

[k-okada]

Sorry, @708yamaguchi please resolve conflicts

[708yamaguchi]

I think the conflict is resolved.

The diff is the following:

• Add README about creating map with fetch
• remove imu_corrector and odom_corrector in fetch_bringup.launch, which exists in fetch.launch too.
  • https://github.com/jsk-ros-pkg/jsk_robot/blob/master/jsk_fetch_robot/jsk_fetch_startup/launch/fetch.launch#L104-L115
  • https://github.com/jsk-ros-pkg/jsk_robot/blob/master/jsk_fetch_robot/jsk_fetch_startup/launch/fetch_bringup.launch#L213-L224
• move slam_karto out of <group if="$(arg launch_move_base)"> because we do not use slam_karto with move_base

[k-okada]

@708yamaguchi please resolve conflicts and remove "PleaseResovleConflicts" label

[708yamaguchi]

I rebased origin/master and I remove PleaseResolveConflicts label.