add arxiv reference

docs/index.rst

@@ -5,7 +5,7 @@
 
 JAX RB: Riemannian Brownian motion on manifolds
 ===============================================
-JAX RB is a library for Riemannian Brownian motion on constrained manifolds embedded in a vector space, or on quotient of such manifolds by a compact group.
+JAX RB is a library for Riemannian Brownian motion on constrained manifolds embedded in a vector space, or on quotient of such manifolds by a compact group. The theory is developed in [NgSo24]_. Please refer to the `github repository <https://github.com/dnguyend/jax-rb>`_ for installation instruction.
 
 .. math::
 .. toctree::
@@ -45,3 +45,6 @@ Indices and tables
    GitHub <https://github.com/dnguyend/jax-rb>
 
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+.. rubric:: References   
+.. [NgSo24] Nguyen, D.; Sommer, S...: Second-order differential operators, stochastic differential equations and Brownian motions on embedded manifolds `arXiv:2406.02879 <https://arxiv.org/abs/2406.02879>`_.