Add simple, minimal example

examples/simple/main.go

@@ -0,0 +1,44 @@
+package main
+
+// A simple program that counts down from 5 and then exits.
+
+import (
+	"fmt"
+	"log"
+	"tea"
+	"time"
+)
+
+type model int
+
+type tickMsg struct{}
+
+func main() {
+	err := tea.NewProgram(model(5), update, view, []tea.Sub{tick}).Start()
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func update(msg tea.Msg, mdl tea.Model) (tea.Model, tea.Cmd) {
+	m, _ := mdl.(model)
+
+	switch msg.(type) {
+	case tickMsg:
+		m -= 1
+		if m <= 0 {
+			return m, tea.Quit
+		}
+	}
+	return m, nil
+}
+
+func view(mdl tea.Model) string {
+	m, _ := mdl.(model)
+	return fmt.Sprintf("Hi. This program will exit in %d seconds...\n", m)
+}
+
+func tick(_ tea.Model) tea.Msg {
+	time.Sleep(time.Second)
+	return tickMsg{}
+}