Add warning about deprecation (#566)

* Add warning about deprecation

* Improve warning text

Co-authored-by: toloudis <toloudis@users.noreply.github.com>

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Co-authored-by: toloudis <toloudis@users.noreply.github.com>

README.md

@@ -1,12 +1,16 @@
 # AICSImageIO
 
+> [!WARNING]  
+> AICSImageIO is now in maintenance mode only.  Please take a look at its compatible successor [`bioio`](https://github.com/bioio-devs/bioio) ([see here for migration guide](https://bioio-devs.github.io/bioio/MIGRATION.html))
+
 [![Build Status](https://github.com/AllenCellModeling/aicsimageio/actions/workflows/build-main.yml/badge.svg)](https://github.com/AllenCellModeling/aicsimageio/actions)
 [![Documentation](https://github.com/AllenCellModeling/aicsimageio/workflows/Documentation/badge.svg)](https://AllenCellModeling.github.io/aicsimageio/)
 [![Code Coverage](https://codecov.io/gh/AllenCellModeling/aicsimageio/branch/main/graph/badge.svg)](https://app.codecov.io/gh/AllenCellModeling/aicsimageio/branch/main)
 [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.4906608.svg)](https://doi.org/10.5281/zenodo.4906608)
 
 Image Reading, Metadata Conversion, and Image Writing for Microscopy Images in Pure Python
 
+
 ---
 
 ## Features