chore: rename keystone to draft

Rename the module, CLI command name, and all references from
keystone/basalt to draft, and fix the stale build/README content
found along the way.

main.go

@@ -1,6 +1,6 @@
 package main
 
-import "gitea.fernandovideira.com/FernandoJVideira/keystone/cmd"
+import "git.fernandovideira.com/FernandoJVideira/draft/cmd"
 
 func main() {
 	cmd.Execute()