misc/trace: add license for the trace-viewer

The trace-viewer doesn't use the Go license, so it makes sense
to include the license text into the README.md file.

While we're at here, reformat existing text using real Markdown
syntax.

Change-Id: I13e42d3cc6a0ca7e64e3d46ad460dc0460f7ed09
Reviewed-on: https://go-review.googlesource.com/9882Reviewed-by: Rob Pike <r@golang.org>

misc/trace/README.md

-This directory contains helper file for trace viewer (go tool trace).
+This directory contains helper file for trace viewer (`go tool trace`).
 
-trace_viewer_lean.html was generated following instructions in:
-https://github.com/google/trace-viewer/wiki/Embedding
-on revision 895aa74558d19d91906fb720df6458244ef160c6 using:
+`trace_viewer_lean.html` was generated by following
+[instructions](https://github.com/google/trace-viewer/wiki/Embedding)
+on revision `895aa74558d19d91906fb720df6458244ef160c6` using:
+```
 trace-viewer$ ./vulcanize_trace_viewer --config=lean
+```
+
+The license for trace-viewer is as follows:
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.