I want to search these repositories which's title contain 'keyword-1' or 'keyword-2' or 'keyword-3'.
I have read the Github search help documents and search api documents, But I still have no idea how to search with multiple keywords.
I think the best way to do that is the way you are demonstrating. I mean just use the tags separated by simple space. I have just tested that the first repositories that are shown are those containing all the tags that I am searching. Give it a try, it must be working just fine