[ruby/securerandom] [DOC] Improve the document about reproducibility …

…of uuid_v7

https://github.com/ruby/securerandom/pull/19/files#r1329476195

ruby/securerandom@156cbb8448

lib/random/formatter.rb

@@ -201,9 +201,8 @@ def uuid
   #
   # The result contains 74 random bits (9.25 random bytes).
   #
-  # Note that this method cannot be made reproducable with Kernel#srand, which
-  # can only affect the random bits.  The sorted bits will still be based on
-  # Process.clock_gettime.
+  # Note that this method cannot be made reproducable because its output
+  # includes not only random bits but also timestamp.
   #
   # See draft-ietf-uuidrev-rfc4122bis[https://datatracker.ietf.org/doc/draft-ietf-uuidrev-rfc4122bis/]
   # for details of UUIDv7.