Update release checklist.
Describe how to update documentation versioning. No need for
sed one-liners each time.
diff --git a/doc/release.txt b/doc/release.txt
index 2003d1d..f72985f 100644
--- a/doc/release.txt
+++ b/doc/release.txt
@@ -9,6 +9,7 @@
- If interfaces were added, increment AGE.
- If interfaces were removed, set AGE to zero.
- Update the version and release date in doc/libogg/*.html.
+ - `make -C doc/libogg update-doc-version`
- Check for uncommitted changes to master.
- Tag the release commit with 'git tag -s vN.M'.
- Include release notes in the tag annotation.
