Mention #11670 and #11745

Author: anatoliykmetyuk

docs/blog/_posts/2021-03-31-scala3-rc2.md

@@ -36,6 +36,11 @@ PR [#9884](https://github.com/lampepfl/dotty/pull/9884) adds a new language feat
 ## Treat Scala.js pseudo-unions as real unions
 In PR [#11671](https://github.com/lampepfl/dotty/pull/11671), we now treat the `scala.scalajs.js.|[A, B]` as if it was a real Scala 3 union `A | B`, which further boosts the support for Scala.js in Scala 3.
 
+## Other API changes
+`-Ycheck-init` was renamed to `-Ysafe-init`. This flag is used to check safe initialization, more about which you can read in the [documentation](https://dotty.epfl.ch/docs/reference/other-new-features/safe-initialization.html). See also PR [#11920](https://github.com/lampepfl/dotty/pull/11920).
+
+PR [#11745](https://github.com/lampepfl/dotty/pull/11745) changes the `compiletime` package API a bit. `compiletime.S` was moved to `compiletime.ops.int.S` and the package object `compiletime` was removed in favor of top-level definitions.
+
 ## Metaprogramming
 The following are some notable metaprogramming changes included into this release: