Other(docs): Add build command to vault-editor readme

utils/vault-editor/README.md

@@ -2,6 +2,8 @@
 
 Bridge uses an encrypted vault to store persistent data. This is a tool for reading and writing this vault.
 
+It can be built with `make vault-editor` in the bridge source code root directory.
+
 Example usage:
 ```bash
 $ ./vault-editor read
@@ -69,4 +71,4 @@ $ ./vault-editor read                       # the vault should have been modifie
     "Installed": true
   }
 }
-```
+```