feat(envc): add support for converting current process environment to YAML

Enhance the `envc convert` command to allow conversion of the current process environment to YAML format. Update README with usage examples and clarify input options. Add tests to ensure correct functionality for environment variable handling.

cmd/envc/convert_test.go

@@ -8,6 +8,33 @@ import (
 	"testing"
 )
 
+func TestRunConvert_EnvironToYAML(t *testing.T) {
+	t.Setenv("ENVC_TEST_PUBLISH", "xyzzy")
+	var stdout, stderr bytes.Buffer
+	code := RunConvert([]string{
+		"--from", "env", "--to", "yaml",
+		"--input", "environ", "--output", "-",
+	}, strings.NewReader(""), &stdout, &stderr)
+	if code != 0 {
+		t.Fatalf("stderr: %s", stderr.String())
+	}
+	out := stdout.String()
+	if !strings.Contains(out, "xyzzy") {
+		t.Fatalf("expected value in yaml out: %s", out)
+	}
+}
+
+func TestRuknConvert_EnvironRequiresFromEnv(t *testing.T) {
+	var stdout, stderr bytes.Buffer
+	code := RunConvert([]string{
+		"--from", "yaml", "--to", "json",
+		"--input", "environ", "--output", "-",
+	}, strings.NewReader(""), &stdout, &stderr)
+	if code != 2 {
+		t.Fatalf("expected exit 2, got %d stderr=%s", code, stderr.String())
+	}
+}
+
 func TestRunConvert_TOMLToJSON(t *testing.T) {
 	var stdout, stderr bytes.Buffer
 	stdin := strings.NewReader("[app]\nport = 8080\n")