docs: improve onboarding (#150)

* docs: improve onboarding

When getting started with go sdk it's easy to miss waiting for initialization. This change will make it easy for newcomers to use the SDK and more advanced users should be able to wait for the readiness in different ways if they don't want to block the main thread

* Add two initialization options

* Fail fast on timeout

.github/workflows/build.yml

@@ -26,6 +26,7 @@ jobs:
       - name: Go vet
         run: go vet ./...
       - name: Run all tests
+        timeout-minutes: 1
         run: go test -race -covermode atomic -coverprofile=profile.cov -v ./...
       - name: Send coverage
         uses: shogo82148/actions-goveralls@v1

README.md

@@ -34,6 +34,7 @@ go get github.com/Unleash/unleash-client-go
 
 The easiest way to get started with Unleash is to initialize it early in your application code:
 
+**Asynchronous initialization example:**
 ```go
 import (
 	"github.com/Unleash/unleash-client-go/v4"
@@ -49,6 +50,26 @@ func init() {
 }
 ```
 
+**Synchronous initialization example:**
+
+```go
+import (
+	"github.com/Unleash/unleash-client-go/v4"
+)
+
+func init() {
+	unleash.Initialize(
+		unleash.WithListener(&unleash.DebugListener{}),
+		unleash.WithAppName("my-application"),
+		unleash.WithUrl("http://unleash.herokuapp.com/api/"),
+		unleash.WithCustomHeaders(http.Header{"Authorization": {"<API token>"}}),
+	)
+
+	// Note this will block until the default client is ready
+	unleash.WaitForReady()
+}
+```
+
 #### Preloading feature toggles
 
 If you'd like to prebake your application with feature toggles (maybe you're working without persistent storage, so Unleash's backup isn't available), you can replace the defaultStorage implementation with a BootstrapStorage. This allows you to pass in a reader to where data in the format of `/api/client/features` can be found.