Add macOS instructions for render_order tutorial

[athenaz2]

🦟 Bug fix

Fixes gazebosim/gazebo_test_cases#1483

Summary

Running simple_demo as per tutorial on macOS with ogre1 as default render engine doesn't work. Added small comment on running with ogre2 for macOS.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
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