Generate project README.md during trellis new

Add README generation with project-specific values (site name, host,
environment URLs) including Requirements, Local development setup,
Deployment, and Documentation sections. Skips if README.md already exists.

Closes #11

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: retlehs

cmd/new.go

@@ -188,6 +188,8 @@ func (c *NewCommand) Run(args []string) int {
 		return 1
 	}
 
+	c.generateReadme(filepath.Join(path, "README.md"))
+
 	fmt.Printf("\n%s project created with versions:\n", color.GreenString(c.name))
 	fmt.Printf("  Trellis %s\n", trellisRelease.Version)
 
@@ -318,6 +320,46 @@ func askHost(ui cli.Ui, t *trellis.Trellis, name string) (host string, err error
 	return result, nil
 }
 
+func (c *NewCommand) generateReadme(path string) {
+	if _, err := os.Stat(path); err == nil {
+		c.UI.Info("Existing README.md detected, skipping generation.")
+		return
+	}
+
+	devHost, _ := c.trellis.HostsFromDomain(c.host, "development")
+	prodHost, _ := c.trellis.HostsFromDomain(c.host, "production")
+
+	readme := fmt.Sprintf(`# %s
+
+| Environment | URL |
+|-------------|-----|
+| Development | http://%s |
+| Production  | http://%s |
+
+## Requirements
+
+- [trellis-cli](https://github.com/roots/trellis-cli) installed
+
+## Local development setup
+
+1. Clone this repository
+2. Run `+"`trellis init`"+` to set up the virtual environment
+3. Run `+"`trellis vm start`"+` to start the development server
+4. Visit [%s](http://%s)
+
+## Deployment
+
+`+"`"+`$ trellis deploy <environment>`+"`"+`
+
+## Documentation
+
+- [Trellis docs](https://roots.io/trellis/docs/)
+- [Bedrock docs](https://roots.io/bedrock/docs/)
+`, c.name, devHost, prodHost, devHost, devHost)
+
+	os.WriteFile(path, []byte(readme), 0644)
+}
+
 func isDirEmpty(name string) (bool, error) {
 	f, err := os.Open(name)
 

cmd/new_test.go

@@ -2,6 +2,8 @@ package cmd
 
 import (
 	"bytes"
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 
@@ -126,3 +128,71 @@ func TestAskDomain(t *testing.T) {
 		})
 	}
 }
+
+func TestGenerateReadme(t *testing.T) {
+	dir := t.TempDir()
+	readmePath := filepath.Join(dir, "README.md")
+
+	ui := cli.NewMockUi()
+	tr := trellis.NewMockTrellis(false)
+	c := NewNewCommand(ui, tr, "1.0.0")
+	c.name = "example.com"
+	c.host = "example.com"
+
+	c.generateReadme(readmePath)
+
+	content, err := os.ReadFile(readmePath)
+	if err != nil {
+		t.Fatalf("could not read README.md: %s", err)
+	}
+
+	readme := string(content)
+
+	requiredStrings := []string{
+		"# example.com",
+		"## Requirements",
+		"## Local development setup",
+		"## Documentation",
+		"http://example.test",
+		"http://example.com",
+		"trellis-cli",
+		"trellis init",
+		"trellis vm start",
+	}
+
+	for _, s := range requiredStrings {
+		if !strings.Contains(readme, s) {
+			t.Errorf("expected README to contain %q", s)
+		}
+	}
+
+	if strings.Contains(readme, "Vagrant") || strings.Contains(readme, "VirtualBox") {
+		t.Error("README should not contain Vagrant/VirtualBox references")
+	}
+}
+
+func TestGenerateReadmeSkipsExisting(t *testing.T) {
+	dir := t.TempDir()
+	readmePath := filepath.Join(dir, "README.md")
+
+	existingContent := "# My custom README\n"
+	os.WriteFile(readmePath, []byte(existingContent), 0644)
+
+	ui := cli.NewMockUi()
+	tr := trellis.NewMockTrellis(false)
+	c := NewNewCommand(ui, tr, "1.0.0")
+	c.name = "example.com"
+	c.host = "example.com"
+
+	c.generateReadme(readmePath)
+
+	content, _ := os.ReadFile(readmePath)
+	if string(content) != existingContent {
+		t.Errorf("existing README was overwritten: got %q, want %q", string(content), existingContent)
+	}
+
+	combined := ui.OutputWriter.String() + ui.ErrorWriter.String()
+	if !strings.Contains(combined, "Existing README.md detected") {
+		t.Error("expected informational message about skipping README generation")
+	}
+}