docs: add note to readme

Author: avik-pal

README.md

@@ -1,5 +1,8 @@
 # SimpleNonlinearSolve.jl
 
+> [!WARNING]
+> This package has been moved into a subpackage in NonlinearSolve (https://github.com/SciML/NonlinearSolve.jl/tree/master/lib/SimpleNonlinearSolve). Direct all questions and issues to NonlinearSolve.jl repository
+
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