dpkg: add -c option (list local deb file contents)

Add example for listing package contents of a downloaded `.deb` file, because `dpkg -L` only works with the `apt` name of the package (and only when installed).

pages/linux/dpkg.md

@@ -4,7 +4,7 @@
 
 - Install a package:
 
-`dpkg -i {{/path/to/file}}`
+`dpkg -i {{path/to/file.deb}}`
 
 - Remove a package:
 
@@ -18,6 +18,10 @@
 
 `dpkg -L {{package_name}}`
 
+- List contents of a local package file:
+
+`dpkg -c {{path/to/file.deb}}`
+
 - Find out which package owns a file:
 
 `dpkg -S {{file_name}}`