man: Itemize dpkg-gensymbols -c levels

This should make it easier to see what each does.

man/dpkg-gensymbols.pod

@@ -219,10 +219,31 @@ symbols are always written to the symbol file template.
 
 Define the checks to do when comparing the generated symbols file with the
 template file used as starting point. By default the level is 1. Increasing
-levels do more checks and include all checks of lower levels. Level 0 never
-fails. Level 1 fails if some symbols have disappeared. Level 2 fails if some
-new symbols have been introduced. Level 3 fails if some libraries have
-disappeared. Level 4 fails if some libraries have been introduced.
+levels do more checks and include all checks of lower levels.
+
+=over
+
+=item Level 0
+
+Never fails.
+
+=item Level 1
+
+Fails if some symbols have disappeared.
+
+=item Level 2
+
+Fails if some new symbols have been introduced.
+
+=item Level 3
+
+Fails if some libraries have disappeared.
+
+=item Level 4
+
+Fails if some libraries have been introduced.
+
+=back
 
 This value can be overridden by the environment variable
 B<DPKG_GENSYMBOLS_CHECK_LEVEL>.