bip-0458: Add entry to the README index

Author: fjahr

README.mediawiki

@@ -1513,6 +1513,13 @@ users (see also: [https://en.bitcoin.it/wiki/Economic_majority economic majority
 | bubb1es, haris
 | Specification
 | Draft
+|-
+| [[bip-0458.mediawiki|458]]
+| Applications
+| Half-Aggregation of BIP 340 Signatures
+| Tim Ruffing, Jonas Nick, Fabian Jahr
+| Specification
+| Draft
 |}
 
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