fix changelog: pod is reader, not writer

I was excited to read in the latest changelog that pandoc could now
write Perl's POD format. But upon further examination, it looks like
v3.6.2 can only read POD, not write it.

Author: mjgardner

changelog.md

@@ -2,7 +2,7 @@
 
 ## pandoc 3.6.2 (2025-01-12)
 
-  * New output format: `pod` (Evan Silberman). Pod ("Plain old documentation")
+  * New input format: `pod` (Evan Silberman). Pod ("Plain old documentation")
     is a markup languaged used principally to document Perl modules and
     programs.