Add SPI build directions and badges (#3)

Author: finestructure

.spi.yml

@@ -0,0 +1,11 @@
+version: 1
+builder:
+  configs:
+  - platform: ios
+    scheme: URLRouting
+  - platform: macos-xcodebuild
+    scheme: URLRouting
+  - platform: tvos
+    scheme: URLRouting
+  - platform: watchos
+    scheme: URLRouting

README.md

@@ -1,5 +1,8 @@
 # swift-url-routing
 
+[![](https://img.shields.io/endpoint?url=https%3A%2F%2Fswiftpackageindex.com%2Fapi%2Fpackages%2Fpointfreeco%2Fswift-url-routing%2Fbadge%3Ftype%3Dswift-versions)](https://swiftpackageindex.com/pointfreeco/swift-url-routing)
+[![](https://img.shields.io/endpoint?url=https%3A%2F%2Fswiftpackageindex.com%2Fapi%2Fpackages%2Fpointfreeco%2Fswift-url-routing%2Fbadge%3Ftype%3Dplatforms)](https://swiftpackageindex.com/pointfreeco/swift-url-routing)
+
 A bidirectional URL router with more type safety and less fuss. This library is built with [Parsing][swift-parsing].
 
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