📝 docs: Update pandoc to match `Setup.hs`

The sdist hook in [Setup.hs](Setup.hs) disables the `smart` extension
when creating man page.

README.md

@@ -210,8 +210,10 @@ or see the [storage bucket listing](https://shellcheck.storage.googleapis.com/in
 
 Distro packages already come with a `man` page. If you are building from source, it can be installed with:
 
-    pandoc -s -t man shellcheck.1.md -o shellcheck.1
+```console
+pandoc -s -f markdown-smart -t man shellcheck.1.md -o shellcheck.1
 sudo mv shellcheck.1 /usr/share/man/man1
+```
 
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