add release notes

Author: rmorshea

docs/source/changelog.rst

@@ -1,6 +1,21 @@
 Changelog
 =========
 
+0.27.0
+------
+
+Introduces changes to the interface for custom Javascript components. This now allows
+JS modules to export a ``mount(element, component, props)`` function which can be used
+to bind new elements to the DOM instead of using the application's own React instance
+and specifying React as a peer dependency. This avoids a wide variety of potential
+issues with implementing custom components and opens up the possiblity for a wider
+variety of component implementations.
+
+- modules with mount func should not have children - :commit:`94d006c`
+- limit to flask<2.0 - :commit:`e7c11d0`
+- federate modules with mount function - :commit:`bf63a62`
+
+
 0.26.0
 ------