Update instructions for including the UI

Makefile

@@ -16,7 +16,7 @@ fuzz :
 pack-web : build-web
 	go run web/pack/main.go
 
-build-web :
+build-web : check-goroot
 	cp $$GOROOT/misc/wasm/wasm_exec.js web/assets/
 	GOOS=js GOARCH=wasm go build -o web/assets/jd.wasm ./web/ui/main.go
 
@@ -82,6 +82,11 @@ ifndef JD_PREVIOUS_VERSION
 	$(error Set JD_PREVIOUS_VERSION for release notes)
 endif
 
+check-goroot:
+ifndef GOROOT
+	$(error Set GOROOT in order to file wasm_exec.js)
+endif
+
 find-issues :
 	-staticcheck ./...
 	-goreportcard-cli -v ./...

main.go

@@ -110,7 +110,7 @@ const (
 
 func serveWeb(port string) error {
 	if serve.Handle == nil {
-		return fmt.Errorf("the web UI wasn't include in this build: use `make release` to include it")
+		return fmt.Errorf("the web UI wasn't include in this build: use `make build` to include it")
 	}
 	http.HandleFunc("/", serve.Handle)
 	log.Printf("Listening on http://localhost:%v...", port)