Reword explicit nulls section

Author: anatoliykmetyuk

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

@@ -31,7 +31,7 @@ There are some notable changes worth mentioning.
 PR [#11920](https://github.com/lampepfl/dotty/pull/11920) restricts usage of experimental features only to nightlies and snapshots. This change ensures that changes deemed experimental will not propagate into the wider ecosystem provided that the wider ecosystem depends on stable releases. This is needed so that if an experimental feature is modified or removed from the language, the ecosystem will not be impacted.
 
 ## New `unsafeNulls` language feature
-PR [#9884](https://github.com/lampepfl/dotty/pull/9884) adds a new language feature which enables explicit nulls checks. From now on, you can use an import `import scala.language.unsafeNulls` to enable the feature, no compiler flags needed. For discussion, see the PR linked above, and for more information on the feature, see the [documentation](https://dotty.epfl.ch/docs/reference/other-new-features/explicit-nulls.html).
+PR [#9884](https://github.com/lampepfl/dotty/pull/9884) adds a new language feature which enables unsafe null operations under explicit nulls. This is a tool to help projects migrating to full explicit nulls gradually. From now on, you can use an import `import scala.language.unsafeNulls` to create an unsafe scope. For discussion, see the PR linked above, and for more information on the feature, see the [documentation](https://dotty.epfl.ch/docs/reference/other-new-features/explicit-nulls.html).
 
 ## 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.