update README.md

Give simple installation instructions

README.md

@@ -4,7 +4,7 @@ Checks current running containers for newer tags according to semver
 
 Usage:
 
-    go run . -h
+    tag-checker -h
 
       -max-pages int
            max number of pages to retrieve from registry (default 10)
@@ -12,3 +12,8 @@ Usage:
            base url of the registry you want to check against (default "https://registry.hub.docker.com")
       -version
            display the version of dockron and exit
+
+
+## Installation
+
+You can either install the binary from the Releases tab or use the image hoated on Docker Hub at `iamthefij/tag-checker`.