Added 'Seeking Maintainers' notice (#1368)

README.md

@@ -1,4 +1,6 @@
-> **Note:** The primary maintainer @acao is on hiatus until December 2020
+# :warning: [Currently Seeking Maintainers](https://github.com/graphql/graphql-playground/issues/1366) :warning:
+
+---
 
 > **SECURITY WARNING:** both `graphql-playground-html` and [all four (4) of it's middleware dependents](#impacted-packages) until `graphql-playground-html@1.6.22` were subject to an  **XSS Reflection attack vulnerability only to unsanitized user input strings** to the functions therein. This was resolved in `graphql-playground-html@^1.6.22`. [More Information](#security-details) [CVE-2020-4038](https://github.com/graphql/graphql-playground/security/advisories/GHSA-4852-vrh7-28rf)