[mirror] Command-line application for uploading a site to a git-pages server

Document `--challenge` option.

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README.md
··· 19 19 Usage 20 20 ----- 21 21 22 + To prepare a DNS challenge for a given site and password: 23 + 24 + ```console 25 + $ git-pages-cli https://mycoolweb.site --password xyz --challenge 26 + mycoolweb.site. 3600 IN TXT "317716dee4379c167e8b5ce9df38eb880e043e5a842d160fe8d5bb408ee0c191" 27 + ``` 28 + 22 29 To deploy a site from a git repository available on the internet (`--password` may be omitted if the repository is allowlisted via DNS): 23 30 24 31 ```console