Of course. In your mainpage.dox (or whatever you call it) put a link to your README.txt in a separate page for oxygen.
\mainpage FooBar
...
\section other_docs Additional Documentation`
...
Key features that distinguish the current release, build instructions,
and a history of Project FooBar are described in the
\ref README "Foobar README file".
and then later, generate this page by creating the README.txt file as a regular text file.
\page README README
\verbinclude README.txt
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