Add comments about auto-generated header files

[AndyZe]

This should help avoid confusion. Fixes #538

[codecov-commenter]

Codecov Report

Merging #539 (1a67795) into master (e7f9962) will decrease coverage by 3.31%.
The diff coverage is 26.60%.

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@@            Coverage Diff             @@
##           master     #539      +/-   ##
==========================================
- Coverage   35.78%   32.48%   -3.31%     
==========================================
  Files         189        7     -182     
  Lines       17570      665   -16905     
  Branches    11592      357   -11235     
==========================================
- Hits         6287      216    -6071     
+ Misses        994      157     -837     
+ Partials    10289      292    -9997     

Flag	Coverage Δ
unittests	32.48% <26.60%> (-3.31%)	⬇️

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Impacted Files	Coverage Δ
...ontroller/test/test_load_diff_drive_controller.cpp	12.50% <0.00%> (ø)
diff_drive_controller/src/odometry.cpp	42.16% <11.11%> (ø)
diff_drive_controller/src/speed_limiter.cpp	46.55% <11.11%> (ø)
...ive_controller/test/test_diff_drive_controller.cpp	17.62% <12.08%> (ø)
...troller/include/diff_drive_controller/odometry.hpp	20.00% <20.00%> (ø)
...iff_drive_controller/src/diff_drive_controller.cpp	39.22% <35.50%> (ø)
...de/diff_drive_controller/diff_drive_controller.hpp	100.00% <100.00%> (ø)
...ectory_controller/test/test_trajectory_actions.cpp
...ntroller/test/test_load_joint_state_controller.cpp
...ory_controller/test/test_trajectory_controller.cpp
... and 191 more