fixes 'catkin_make install' problem

[teevr]

I wanted to install/run ocam with catkin_make install but failed as followings;

teevr@teevr-NUC7i7BNH:~/ws$ catkin_make install
......
teevr@teevr-NUC7i7BNH:~/ws$ . install/setup.sh
teevr@teevr-NUC7i7BNH:~/ws$ roslaunch ocam ocam_ros.launch
RLException: [ocam_ros.launch] is neither a launch file in package [ocam] nor is [ocam] a launch file name
The traceback for the exception was written to the log file
1 teevr@teevr-NUC7i7BNH:~/ws$

This PR makes catkin_make install work properly, i guess.

[zeropk]

first, check if the ros package is added
$ rospack list | grep ocam

if ros package is added

$ source devel/setup.bash
$ roslaunch ocam ocam_ros.launch

if ros package is not added try build again
check the link for oCam ROS Package
https://github.com/withrobot/oCam/tree/master/Software/oCam_ROS_Package

[teevr]

@zeropk oh, i was able to run with commands catkin_make, source devel/setup.sh and roslaunch ocam ocam_ros.launch.
but failed with catkin_make install, source install/setup.sh and roslaunch ocam ocam_ros.launch (this should work for packaging or something, i think).

[zeropk]

oCam ROS Package does not include setup for catkin_make install, we recommend using catkin_make.
If you want to use you edit ocam/CMakeLists.txt.

[teevr]

ok. what i'm saying is this PR can solve the 'install' problem above.
i've tested on ROS noetic.
so i want this PR merged (iff there's no flaw).