[inplace.vector.modifiers] Harmonize wording for returned iterator

Author: tkoeppe

source/containers.tex

@@ -10004,8 +10004,9 @@
 
 \pnum
 \returns
-%FIXME: Should this be "An iterator past the last inserted element of rg."?
-Iterator past last inserted element of \tcode{rg}.
+An iterator pointing to the first element of \tcode{rg}
+that was not inserted into \tcode{*this},
+or \tcode{ranged::end(rg)} if no such element exists.
 
 \pnum
 \complexity