Dpkg::Checksums: Mention that add_from_file is used to verify digests too

Make it explicit in the sub description.

Prompted-by: Johannes Schauer <josch@debian.org>

debian/changelog

@@ -64,6 +64,8 @@ dpkg (1.18.11) UNRELEASED; urgency=medium
       poorly on many technical terms.
     - Append the German man pages addendum at the end of the translation,
       instead of assuming that every page has the SEE ALSO section.
+    - Explicitly mention that Dpkg::Checksums::add_from_file() is used to
+      verify digests too. Prompted by Johannes Schauer <josch@debian.org>.
   * Build system:
     - Add support for profiling perl modules.
     - Clean up compiler and linker automatic flag usage in configure.

scripts/Dpkg/Checksums.pm

@@ -155,9 +155,9 @@ sub reset {
 
 =item $ck->add_from_file($filename, %opts)
 
-Add checksums information for the file $filename. The file must exists
-for the call to succeed. If you don't want the given filename to appear
-when you later export the checksums you might want to set the "key"
+Add or verify checksums information for the file $filename. The file must
+exists for the call to succeed. If you don't want the given filename to
+appear when you later export the checksums you might want to set the "key"
 option with the public name that you want to use. Also if you don't want
 to generate all the checksums, you can pass an array reference of the
 wanted checksums in the "checksums" option.