ARROW-11650: [Rust][DataFusion] Add Postgres License

LICENSE.txt

@@ -2193,3 +2193,34 @@ The files in cpp/src/arrow/vendored/fast_float/ contain code from
 https://github.com/lemire/fast_float
 
 which is made available under the Apache License 2.0.
+--------------------------------------------------------------------------------
+
+DataFusion aims to support the PostgreSQL compatibility. To achieve compatibility
+parts of the DataFusion code base may have reproduced code and documentation from the
+PostgreSQL project and are subject to the following license.
+
+  PostgreSQL Database Management System
+  (formerly known as Postgres, then as Postgres95)
+
+  Portions Copyright © 1996-2021, The PostgreSQL Global Development Group
+
+  Portions Copyright © 1994, The Regents of the University of California
+
+  Permission to use, copy, modify, and distribute this software and its
+  documentation for any purpose, without fee, and without a written
+  agreement is hereby granted, provided that the above copyright notice
+  and this paragraph and the following two paragraphs appear in all
+  copies.
+
+  IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
+  FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
+  INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
+  DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF
+  THE POSSIBILITY OF SUCH DAMAGE.
+
+  THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
+  INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+  AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
+  ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS
+  TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR
+  MODIFICATIONS.