[Doc] Add proj_size < hidden_size in LSTM (#106364)
Summary:
Add parameter constraint: `proj_size` has to be smaller than `hidden_size` in RNNBase doc.
Ref:
https://github.com/pytorch/pytorch/blob/ceea08a986805030014fac203d5b2411e23ff091/torch/nn/modules/rnn.py#L83
https://github.com/pytorch/pytorch/blob/ceea08a986805030014fac203d5b2411e23ff091/torch/nn/modules/rnn.py#L458
Test Plan: Please see GitHub Actions.
Differential Revision: D47943365
Fix: #105628
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106364
Approved by: https://github.com/mikaylagawarecki
