Update README.md

Author: CosmicCrusader23

README.md

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 # IB Revision Bank
 
-Curated, merged question bank for IB Mathematics (AA & AI), IB Physics, IB Chemistry and IB Economics —
+Curated, merged question bank for IB Mathematics (AA & AI), IB Physics, IB Chemistry, IB Biology, IB ESS, and IB Economics —
 pulled from publicly available revision sources and grouped by syllabus topic.
 
 **Live:** https://ib.mycosmic.dev/