Update header level for BAE information

Author: wang-chen

README.md

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   <img src="https://raw.githubusercontent.com/sair-lab/bae/93eb45121965719c1abbed9437b4832f669b8c87/assets/github-banner.svg" alt="bundle adjustment in the eager-mode" width="100%" />
 </picture>
 
-# BAE has been merged into PyPose and is available from [v0.9.5](https://pypi.org/project/pypose/) or higher. Please refer to [this example](https://github.com/pypose/pypose/tree/main/examples/module/ba) and docs of [psjac](https://pypose.org/docs/main/generated/pypose.autograd.function.parallel_for_sparse_jacobian/#pypose.autograd.function.parallel_for_sparse_jacobian) and [LM](https://pypose.org/docs/main/generated/pypose.optim.LevenbergMarquardt/#pypose.optim.LevenbergMarquardt).
+## BAE has been merged into PyPose and is available from [v0.9.5](https://pypi.org/project/pypose/) or higher. Please refer to [this example](https://github.com/pypose/pypose/tree/main/examples/module/ba) and docs of [psjac](https://pypose.org/docs/main/generated/pypose.autograd.function.parallel_for_sparse_jacobian/#pypose.autograd.function.parallel_for_sparse_jacobian) and [LM](https://pypose.org/docs/main/generated/pypose.optim.LevenbergMarquardt/#pypose.optim.LevenbergMarquardt).
 
 
 ### BAE is published as the following paper: