Add version of symlink :absolute flag introduction

Author: m-dango

doc/Type/IO/Path.pod6

@@ -998,7 +998,8 @@ does not exist, creates a dangling symbolic link.
 
 C<symlink> creates a symbolic link using an absolute path
 by default. To create a relative symlink set the C<absolute>
-parameter to C<False> e.g. C<:!absolute>.
+parameter to C<False> e.g. C<:!absolute>. This flag was
+introduced in Rakudo version 2020.11.
 
 To create a hard link, see L«C<link>|/routine/link».