Update README.md

Author: FabsOliveira

README.md

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+# Notice: this is out of date!
+This repository has been archived in October 2024. The new version of the linear optimisation notes can be found at: [github.com/gamma-opt/linpot-notes](https://github.com/gamma-opt/linopt-notes)
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 # Optimisation notes
 
 Download the notes here: [download](https://gamma-opt.github.io/optimisation-notes/pdfs/optimisation-notes.pdf)