Document RAKU_REPL_OUTPUT_METHOD

Author: lizmat

doc/Programs/03-environment-variables.rakudoc

@@ -129,7 +129,17 @@ X<|Programs,RAKUDO_LOG_PRECOMP>
 If set to 1, diagnostic information about the precompilation process is
 emitted.
 
-=head2 Line editor
+=head2 REPL (Read Eval Print Loop)
+
+X<|Programs,RAKU_REPL_OUTPUT_METHOD>
+=item C<RAKU_REPL_OUTPUT_METHOD>
+
+This specifies the name of the method that should be called on the result
+value of a statement in the REPL if the statement did B<not> cause any
+output of its own.  If absent, C<gist> will be assumed.  One can use
+C<raku> to force a more literal, parsable representation.  Or C<Str> to force a
+complete string representation.  Available as of the 2020.06 release of
+the Rakudo compiler.
 
 X<|Programs,RAKUDO_LINE_EDITOR>
 =item C<RAKUDO_LINE_EDITOR>