Update README (#18)

fixing typo in SwiftPrometheus

Author: tonyalbor

README.md

@@ -6,7 +6,7 @@ A prometheus client for Swift supporting counters, gauges, histograms, summaries
 
 # Installation
 
-SwiftPormetheus is available through SPM. To include it in your project add the following dependency to your `Package.swift`:
+SwiftPrometheus is available through SPM. To include it in your project add the following dependency to your `Package.swift`:
 ```swift
         .package(url: "https://github.com/MrLotU/SwiftPrometheus.git", from: "1.0.0-alpha")
 ```