Add a reminder to review libtool version info before the release

It would have been better to do it before 3.2.3 rather than after, but
still better to do it before 3.2.4 than never.

Author: vadz

docs/contributing/how-to-release.md

@@ -54,6 +54,10 @@ the micro version of this release. If this release represents a major
 or minor release, these changes will have to be performed manually at
 this point.
 
+Also review the version information in `build/bakefiles/version.bkl`: if any
+new APIs have been added in this release, the "current" and "age" fields must
+be incremented and "revision" reset to 0.
+
 Note that the best order depends on the release being prepared: for a
 development release, `docs/publicity/announce.txt` contains the list of the
 major changes since the last stable release and should be updated first, as