docs: Add note on addition of new shared boot info

Adds a note that there is now additional information that can
(optionally) be provided via shared boot information.

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
diff --git a/docs/release-notes.d/data-sharing.md b/docs/release-notes.d/data-sharing.md
new file mode 100644
index 0000000..767aaad
--- /dev/null
+++ b/docs/release-notes.d/data-sharing.md
@@ -0,0 +1,2 @@
+- Added currently running slot ID and maximum application size to
+  shared data function definition.