update some errors I encountered

Author: haifengkao

README.md

@@ -162,6 +162,15 @@ Since Xcode 11.4, you may use its built-in support for sourcekit-lsp
 }
 ```
 
+### Build failed? What should I do?
+Go to vscode `OUTPUT` window, then select `SPM`. The `OUTPUT` window will tell you what's wrong.
+
+### Database is locked??
+If you saw
+```
+database is locked Possibly there are two concurrent builds running in the same filesystem location
+```
+it means swift package manager tries to access frameworks built by `New Build System`. Open your Xcode's `Workspace Settings...`, select `Legacy Build System` and rebuid the framework.
 
 ### Other questions?