Update README.md

Author: AntonOresten

README.md

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-Einops.jl is a Julia implementation of the [einops](https://einops.rocks) Python package, providing an elegant and intuitive notation for tensor operations. Einops offers a unified way to perform Julia's `reshape` and `permutedims`, with plans for also implementing `reduce` and `repeat`.
+> [!WARNING]  
+> This package is still under development, and does not implement all of the features of the original (see [Roadmap](#Roadmap)).
+
+Einops.jl is a Julia implementation of the [einops](https://einops.rocks) Python package, providing an elegant and intuitive notation for tensor operations. `rearrange` offers a unified way to perform Julia's `reshape` and `permutedims`, with plans for also implementing `reduce` and `repeat`.
 
 The Python implementation uses strings to specify the operation, but that would be tricky to compile in Julia, so a string macro `@einops_str` is exported for parity, e.g. `einops"a 1 b c -> (c b) a"`, which expands to the form `(:a, 1, :b, :c,) --> ((:c, :b), :a)` where `-->` is an operator that creates an `Einops.Pattern{(:a, 1, :b, :c), ((:c, :b), :a)}`, allowing for compile-time awareness of dimensionalities and permutations—this is not yet taken advantage of, since the tuple types are sufficient for at least ensuring type stability (see [Roadmap](#Roadmap)).