Start 1.1.8 release notes

Just so I don't forget this bug fix.

(The bug is in one of the dependencies, so it will actually be fixed
only once dependencies are bumped again.)

release-notes/1.1.8.txt

@@ -0,0 +1,5 @@
+NEW:
+  -
+
+FIXED:
+  - Fix mp2-in-mkv decoding on Windows