CHANGELOG.md: Add SE-0193

Author: slavapestov

CHANGELOG.md

@@ -61,6 +61,18 @@ Swift 5.0
 Swift 4.2
 ---------
 
+* [SE-0193][]
+
+  Various function-like declarations can now be marked as `@inlinable`,
+  making their bodies available for optimizations from other modules.
+
+  Inlinable function bodies must only reference public declarations, unless
+  the referenced declaration is marked as `@usableFromInline`.
+
+  Note that the presence of the attribute itself does not force inlining or
+  any other optimization to be performed, nor does it have any effect on
+  optimizations performed within a single module.
+
 * The C `long double` type is now imported as `Float80` on i386 and x86_64
   macOS and Linux. The tgmath functions in the Darwin and glibc modules now
   support `Float80` as well as `Float` and `Double`. Several tgmath