Update README

apriltag_imu/sim/README

-Nicer demos:
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-circle.bag: flat circle in Z plane, IMU NOT biased
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-circleXYZ.bag: bended circle with sinusoidal deviation in 3 directions, IMU NOT biased
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-everything: alike circleXYZ with orientation changes and IMU noise, IMU biased on all axis
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-everythingBiasedX: alike everything with orientation changes and IMU noise, IMU biased on X axis
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apriltag_imu/sim/README.md

+# Simulation demos:
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+- **circle.bag:** Flat circle in Z plane. IMU without noise and not biased.
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+- **wave.bag:** Bended circle with sinusoidal translation in Z. IMU without noise and not biased. (old name circleXYZ.bag)
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+- **wave_noiseXYZ_biasY:** Bended circle with sinusoidal translation in Z. IMU with noise and biased only on Y axis (accel. and gyro.). (old name everythingBiasedX.bag)
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+- **wave_noiseXYZ_biasXYZ:** Bended circle with sinusoidal translation in Z. IMU with noise and biased. (old name everything.bag)
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