docs/command-reference.md: fix markdown

Signed-off-by: Akihiro Suda <[email protected]>

Author: AkihiroSuda

docs/command-reference.md

@@ -5,9 +5,9 @@
 :nerd_face: = nerdctl specific
 
 > [!NOTE]
-- Unlisted `docker` CLI flags are unimplemented yet in `nerdctl` CLI.
-  It does not necessarily mean that the corresponding features are missing in containerd.
-- Some commands and flags are only available on Linux.
+> - Unlisted `docker` CLI flags are unimplemented yet in `nerdctl` CLI.
+>   It does not necessarily mean that the corresponding features are missing in containerd.
+> - Some commands and flags are only available on Linux.
 
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