Help: add release notes for NAMELINK_COMPONENT

Help/release/dev/namelink-component.rst

@@ -0,0 +1,7 @@
+namelink-component
+------------------
+
+* The :command:`install` command learned an optional ``NAMELINK_COMPONENT``
+  parameter, which allows you to change the component for a shared library's
+  namelink. If none is specified, the value of ``COMPONENT`` is used by
+  default.