Add authors and contributors files.

AUTHORS.txt

+# This is the official list of SwiftShader authors for copyright purposes.
+# This file is distinct from the CONTRIBUTORS files.
+# See the latter for an explanation.
+# Names should be added to this file as:
+# Name or Organization <email address>
+# The email address is not required for organizations.
+
+Google Inc.
+The ANGLE Project Authors <angleproject@googlegroups.com>
\ No newline at end of file

CONTRIBUTORS.txt

+# People who have agreed to one of the CLAs and can contribute patches.
+# The AUTHORS file lists the copyright holders; this file
+# lists people.  For example, Google employees are listed here
+# but not in AUTHORS, because Google holds the copyright.
+#
+# https://developers.google.com/open-source/cla/individual
+# https://developers.google.com/open-source/cla/corporate
+#
+# Names should be added to this file as:
+#     Name <email address>
+
+Google Inc.
+ Nicolas Capens <capn@google.com>
+ Alexis Htu <sugoi@google.com>
+ Shannon Woods <shannonwoods@google.com>
+ Corentin Wallez <cwallez@google.com>
+ Greg Hartman <ghartman@google.com>
+ Ping-Hao Wu <pinghao@google.com>
+ Maxime Grgoire <mgregoire@google.com>
+ Veranika Liaukevich <veranika@google.com>
+ John Bauman <jbauman@google.com>
+ Keun Soo Yim <yim@google.com>
+ John Sheu <sheu@google.com>
+ Philippe Hamel <hamelphi@google.com>
+ Daniel Toyama <kenjitoyama@google.com>
\ No newline at end of file