Document the C<loop> statement

... by shamelessly copying the text from the spec....

lib/Language/control.pod

@@ -136,11 +136,23 @@ specify a final value for the block.
     }
     #-> Int
 
-=begin comment
-
 =head2 loop
 
-=end comment
+The C<loop> statement is the C-style C<for> loop in disguise:
+
+    loop (my $i = 0; $i < 10; $i++) {
+        ...
+    }
+
+As in C, the parentheses are required if you supply the 3-part spec;
+however, the 3-part loop spec may be entirely omitted to write an infinite
+loop.  That is,
+
+    loop {...}
+
+is equivalent to the C-ish idiom:
+
+    loop (;;) {...}
 
 =head2 repeat/while, repeat/until