feat: look for repos in the usual folders, not just ~/git (#57)

Without roots in the config, repos are found under whichever of ~/git,
~/repo, ~/repos, ~/projects, ~/code, ~/source and ~/src exist. Missing
ones cost a stat each. A root that's a symlink to another is scanned
once, and a repo under two roots keeps the first one's name.

Reviewed-on: #57
Co-authored-by: Karl-Einar Bergstrøm <karl-einarb@outlook.com>

cmd/lazysecrets/main.go

@@ -287,7 +287,7 @@ Flags:
 			if start == "" {
 				start, _ = os.Getwd()
 			}
-			roots := []string{"~/git"}
+			roots := repo.DefaultRoots
 			if pc.Repos.Roots != nil {
 				roots = *pc.Repos.Roots
 			}