Update README.md

Author: CodingMarkus

README.md

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+# End of Life Notice
+
+It was a fun project and I learned a lot, but I had to disabbondan this project for various reasons:
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+* POSIX shell scripting has no local variables, and constantly working with sub-shells kills any performance.
+* Performance in general became more and more of a problem.
+* Testability became more difficult, and I started with a bad unit test strategy.
+* After trying to solve [Advent of Code 2023](https://github.com/CodingMarkus/Advent-of-Code-Solutions) in the POSIX shell only, I learned a lot of new tricks and wasn't happy with the code design of that project.
+* In the end, it's just not worth the effort, since my original goal was to make other scripting languages irrelevant in many cases just by using powerful POSIX shell scripts, but to run those shells you need the full POSIX environment, and that may be more complicated than just having a single portable interpreter for another scripting language.
+
+---
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 # POSIX Shell Script Tools
 
 A collection of functions and modules to write powerful POSIX shell scripts.