Add acknowledgments and license for rb-readline

Author: aycabta

README.md

@@ -11,3 +11,7 @@ Reline is compatible with the API of Ruby's stdlib 'readline', GNU Readline and
 ## License
 
 The gem is available as open source under the terms of the [Ruby License](https://www.ruby-lang.org/en/about/license.txt).
+
+## Acknowledgments for [rb-readline](https://github.com/ConnorAtherton/rb-readline)
+
+In developing Reline, we have used some of the rb-readline implementation, so this library includes [copyright notice, list of conditions and the disclaimer](license_of_rb-readline) under the 3-Clause BSD License. Reline would never have been developed without rb-readline. Thank you for the tremendous accomplishments.

license_of_rb-readline

@@ -0,0 +1,25 @@
+Copyright (c) 2009, Park Heesob
+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 Park Heesob 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.

reline.gemspec

@@ -14,7 +14,7 @@ Gem::Specification.new do |spec|
   spec.homepage      = 'https://github.com/ruby/reline'
   spec.license       = 'Ruby'
 
-  spec.files         = Dir['BSDL', 'COPYING', 'README.md', 'lib/**/*']
+  spec.files         = Dir['BSDL', 'COPYING', 'README.md', 'license_of_rb-readline', 'lib/**/*']
   spec.require_paths = ['lib']
 
   spec.required_ruby_version = Gem::Requirement.new('>= 2.5')