Add release notes for -disabledeprecation removal

doc/release-notes.md

@@ -4,3 +4,23 @@ release-notes at release time)
 Notable changes
 ===============
 
+`-disabledeprecation` removal
+-----------------------------
+
+In release 1.0.9 we implemented automatic deprecation of `zcashd` software
+versions made by the Zcash Company. The configuration option
+`-disabledeprecation` was added as a way for users to specifically choose to
+stay on a particular software version. However, it incorrectly implied that
+deprecated releases would still be supported.
+
+This release removes the `-disabledeprecation` option, so that `zcashd` software
+versions made by the Zcash Company will always shut down in accordance with the
+defined deprecation policy (currently 16 weeks after release). Users who wish to
+use a different policy must now specifically choose to either:
+
+- edit and compile the source code themselves, or
+- obtain a software version from someone else who has done so (and obtain
+  support from them).
+
+Either way, it is much clearer that the software they are running is not
+supported by the Zcash Company.