Fix error message and add README section (#22)

Author: mnuttall

README.md

@@ -39,3 +39,29 @@ $ TEST_GITHUB_TOKEN=<a valid github auth token> go test ./...
 
 Note that the tests in pkg/git/repository_test.go will clone and manipulate a
 remote Git repository locally.
+
+To run a particular test: for example, 
+
+```shell
+go test ./pkg/git -run TestCopyServiceWithFailureCopying
+```
+
+## Getting started
+
+This section is temporary. To create a sample promotion Pull Request, until https://github.com/rhd-gitops-example/services/issues/8 is done:
+
+- Copy https://github.com/mnuttall/gitops-repo-testing 
+- Copy https://github.com/mnuttall/staging
+- Build the code: `go build ./cmd/services`
+- export GITHUB_TOKEN=[your token]
+- Substitute your repository URLs for those in square brackets:
+
+```shell
+./services promote --from [https://github.com/mnuttall/gitops-repo-testing] --to [https://github.com/mnuttall/staging] --service service-a`
+```
+
+We need to remove the local cache between requests. See https://github.com/rhd-gitops-example/services/issues/20. Until then, add `rm -rf ~/.promotion/cache; ` before subsequent requests.
+
+New pull requests need new branches. Add `--branch [unique branch name]` before submitting further promotion PRs. See https://github.com/rhd-gitops-example/services/issues/21.
+
+See https://github.com/rhd-gitops-example/services/issues/19 for an issue related to problems 'promoting' config from a source repo into a gitops repo. 

pkg/avancement/service_manager.go

@@ -88,7 +88,7 @@ func (s *ServiceManager) Promote(serviceName, fromURL, toURL, newBranchName stri
 func (s *ServiceManager) checkoutSourceRepo(repoURL, branch string) (git.Repo, error) {
 	repo, err := s.cloneRepo(repoURL, branch)
 	if err != nil {
-		return nil, fmt.Errorf("failed to clone destination repo %s: %w", repoURL, err)
+		return nil, fmt.Errorf("failed to clone source repo %s: %w", repoURL, err)
 	}
 	err = repo.Checkout(branch)
 	if err != nil {