Improve doc strings (#518)

python/sglang/srt/constrained/fsm_cache.py

@@ -1,3 +1,4 @@
+"""Cache for the compressed finite state machine."""
 from sglang.srt.constrained import RegexFSM, TransformerTokenizer
 from sglang.srt.constrained.base_cache import BaseCache
 

python/sglang/srt/constrained/jump_forward.py

@@ -1,3 +1,7 @@
+"""
+Faster constrained decoding.
+Reference: https://lmsys.org/blog/2024-02-05-compressed-fsm/
+"""
 import interegular
 
 from sglang.srt.constrained import FSMInfo, disk_cache, make_deterministic_fsm