Update README.md

[MigVega]

Adding link to OGM2PGBM
to enable SLAM_toolbox for localization from an occupancy grid map

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Basic Info

Info	Please fill out this column
Ticket(s) this addresses	(add tickets here #1)
Primary OS tested on	(Ubuntu, MacOS, Windows)
Robotic platform tested on	(Steve's Robot, gazebo simulation of Tally, hardware turtlebot)

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Description of contribution in a few bullet points

Description of documentation updates required from your changes

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Future work that may be required in bullet points

[SteveMacenski]

That's a neat tool, but I don't want to point to specific implementations outside of what I have personal experience using in a production setting to make sure there is excellent user experience for anything I'm passively endorsing in documentation.

My closing of this PR is not a indication of the quality or functionality of your tool - it may be absolutely perfect for what you describe. I'm just not comfortable "vendorizing" something like that without a much larger degree of due diligence.