coreutils commands: move pages to common/ folder (#2442)

pages/common/dirname.md

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+# dirname
+
+> Calculates the parent directory of a given file or directory path.
+
+- Calculate the parent directory of a given path:
+
+`dirname {{path/to/file_or_directory}}`
+
+- Calculate the parent directory of multiple paths:
+
+`dirname {{path/to/file_a}} {{path/to/directory_b}}`
+
+- Delimit output with a NUL character instead of a newline (useful when combining with `xargs`):
+
+`dirname --zero {{path/to/directory_a}} {{path/to/file_b}}`