Add SPI badges (#3)

Author: finestructure

README.md

@@ -1,5 +1,8 @@
 # vapor-routing
 
+[![](https://img.shields.io/endpoint?url=https%3A%2F%2Fswiftpackageindex.com%2Fapi%2Fpackages%2Fpointfreeco%2Fvapor-routing%2Fbadge%3Ftype%3Dswift-versions)](https://swiftpackageindex.com/pointfreeco/vapor-routing)
+[![](https://img.shields.io/endpoint?url=https%3A%2F%2Fswiftpackageindex.com%2Fapi%2Fpackages%2Fpointfreeco%2Fvapor-routing%2Fbadge%3Ftype%3Dplatforms)](https://swiftpackageindex.com/pointfreeco/vapor-routing)
+
 A routing library for [Vapor][vapor] with a focus on type safety, composition, and URL generation.
 
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