Add example for custom configurations

CONTRIBUTING.md

@@ -28,7 +28,7 @@ make setup
 ### Running gaper in development
 
 ```
-make build && ./gaper --verbose --bin-name srv --build-path ./testdata/server
+make build && ./gaper --verbose --bin-name srv --build-path ./testdata/server --build-args="-ldflags=\"-X 'main.Version=v1.0.0'\""
 ```
 
 ### Running lint

README.md

@@ -98,6 +98,16 @@ Using all defaults provided by Gaper:
 gaper
 ```
 
+Example providing a few custom configurations:
+
+```
+gaper \
+	--bin-name build/api-dev \
+	--build-path cmd/server \
+	--build-args "-ldflags=\"-X 'main.Version=dev'" \
+	--watch .
+```
+
 Ignore watch over all test files:
 
 > no need for this if you have not disabled the default ignore settings `--disable-default-ignore`

testdata/server/main.go

@@ -7,6 +7,8 @@ import (
 	"net/http"
 )
 
+var Version string
+
 func main() {
 	http.HandleFunc("/foo", func(w http.ResponseWriter, r *http.Request) {
 		fmt.Fprintf(w, "Hello, %q", html.EscapeString(r.URL.Path)) // nolint gas
@@ -16,6 +18,6 @@ func main() {
 		log.Fatal("Forced failure")
 	})
 
-	log.Println("Starting server")
+	log.Println("Starting server: Version", Version)
 	log.Fatal(http.ListenAndServe(":8080", nil))
 }