Update readme and SECURITY.md

CHANGELOG.md

@@ -6,6 +6,7 @@ Exclamation symbols (:exclamation:) note something of importance e.g. breaking c
 ## [Unreleased]
 ### Added
 ### Changed
+- Touched up readme including header and badges.
 ### Deprecated
 ### Removed
 - Abstract methods from `InputMedia` interface, as method annotations didn't work for propagation.

SECURITY.md

-# Security
+# Security Policy
 
-To report a security vulnerability, please use the [Tidelift security contact](https://tidelift.com/security).
-Tidelift will then coordinate the fix and disclosure.
+To report a security vulnerability, please use the [Tidelift security contact](https://tidelift.com/security). Tidelift will coordinate the fix and disclosure.