Add new breaking change note to Gerrit v3.10 release notes

The Change 400622 breaks the binary compatibility with all
plugins exposing SSH commands. Add the note into the breaking
changes section.

Change-Id: I064679d1c6dac91c58db352800bae1b3cb65270a
diff --git a/pages/site/releases/3.10.md b/pages/site/releases/3.10.md
index 8c75bb4..650c9df 100644
--- a/pages/site/releases/3.10.md
+++ b/pages/site/releases/3.10.md
@@ -259,6 +259,21 @@
 
   The 50MB limit is hardcoded and cannot be changed via configuration.
 
+* [Change 400622](https://gerrit-review.googlesource.com/400622):
+`PluginCommandModule` requires the plugin name in its constructor, hence all plugins
+that expose SSH commands need amending with an explicit constructor like
+the following:
+
+  ```java
+  class MySshModule extends PluginCommandModule {
+
+    @Inject
+    MySshModule(@PluginName String pluginName) {
+      super(pluginName);
+    }
+  }
+  ```
+
 ### Other changes
 
 * [Change 409729](https://gerrit-review.googlesource.com/409729):