Add IJG LICENSE file

LICENSE-IJG

@@ -0,0 +1,69 @@
+jpeg-encoder IJG License
+========================
+
+The jpeg-encoder crate declares license "(MIT OR Apache-2.0) AND IJG".
+The published crate includes MIT and Apache license files, but it does not
+currently include a top-level IJG license file. This Chromium-local file
+documents the IJG terms for the IJG-derived portions of jpeg-encoder until the
+crate publishes the missing license file upstream.
+
+The IJG-derived portions include, at least:
+
+- src/fdct.rs, which is ported from mozjpeg to Rust and states that it was part
+  of the Independent JPEG Group's software.
+- src/avx2/fdct.rs, which is ported from mozjpeg / jfdctint-avx2.asm to Rust
+  and states that it is based on the x86 SIMD extension for the IJG JPEG
+  library.
+
+In the IJG terms below, "this software" refers to the IJG-derived portions of
+jpeg-encoder listed above, not to the jpeg-encoder crate as a whole. The rest
+of jpeg-encoder remains covered by the crate's MIT OR Apache-2.0 terms.
+
+Conditions of distribution and use
+==================================
+
+In plain English:
+
+1. We don't promise that this software works.  (But if you find any bugs,
+   please let us know!)
+2. You can use this software for whatever you want.  You don't have to pay us.
+3. You may not pretend that you wrote this software. If you use it in a
+   program, you must acknowledge somewhere in your documentation that
+   you've used the IJG code.
+
+In legalese:
+
+The authors make NO WARRANTY or representation, either express or implied,
+with respect to this software, its quality, accuracy, merchantability, or
+fitness for a particular purpose.  This software is provided "AS IS", and you,
+its user, assume the entire risk as to its quality and accuracy.
+
+This software is copyright (C) 1991-2020, Thomas G. Lane, Guido Vollbeding.
+All Rights Reserved except as specified below.
+
+Permission is hereby granted to use, copy, modify, and distribute this
+software (or portions thereof) for any purpose, without fee, subject to these
+conditions:
+(1) If any part of the source code for this software is distributed, then this
+README file must be included, with this copyright and no-warranty notice
+unaltered; and any additions, deletions, or changes to the original files
+must be clearly indicated in accompanying documentation.
+(2) If only executable code is distributed, then the accompanying
+documentation must state that "this software is based in part on the work of
+the Independent JPEG Group".
+(3) Permission for use of this software is granted only if the user accepts
+full responsibility for any undesirable consequences; the authors accept
+NO LIABILITY for damages of any kind.
+
+These conditions apply to any software derived from or based on the IJG code,
+not just to the unmodified library.  If you use our work, you ought to
+acknowledge us.
+
+Permission is NOT granted for the use of any IJG author's name or company name
+in advertising or publicity relating to this software or products derived from
+it. This software may be referred to only as "the Independent JPEG Group's
+software".
+
+We specifically permit and encourage the use of this software as the basis of
+commercial products, provided that all warranty or liability claims are
+assumed by the product vendor.