Created Usage (markdown)

Usage.md

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+# CLI Usage
+
+## Import a single URL or list of URLs via stdin
+```bash
+echo 'https://example.com' | ./archive
+# or
+./archive < urls_to_archive.txt
+```
+
+## Import a bookmarks export from a browser
+```bash
+./archive ~/Downloads/bookmarks_export.html
+```
+
+## Archive URLs from a remote RSS feed or file
+```bash
+./archive https://example.com/feed.rss
+# or
+./archive https://example.com/links.txt
+```