Change the README file format from rdoc to markdown, and add the description.

README.md

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+# Redmine Glossary Plugin
+
+This is a plugin for Redmine to create a glossary that is a list of terms in a project.
+
+This is a remake version of [the original glossary plugin](https://ja.osdn.net/projects/rp-glossary/releases/). The main goal of remaking is to fit for the recent redmine version to be maintainable.
+
+## The use
+
+- Management of technical terms in a system analysis phase
+- Interlinear translation table
+- Translate table from term to data type (class name)
+- Management of naming examples in a coding
+
+## To get
+
+### Repository
+
+- <https://github.com/torutk/redmine_glossary>
+
+The branches are as follows:
+
+- __master__ for the recent Redmine version
+- __development__ under developping for the next release
+- __support/2.x__ original glossary plugin ported for Redmine 2.x
+- __support/3.x__ original glossary plugin ported for Redmine 3.x
+- __support/4.0or1/based_original__ original glossary plugin ported for Redmine 4.0 or 4.1
+
+### Installation and Setup
+
+1. Copy the plugin directory into the Redmine's plugin directory. Note that the name of plugin's directory should be "redmine_glossary".
+2. Migrate plugin task.
+3. Restart the redmine.
+4. Set permission of glossary plugin in "Administration > Roles and permissions"
+
+### Uninstall
+
+- rails redmine:plugins:migrate NAME=redmine_glossary VERSION=0
+
+

README.rdoc

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-= redmine_glossary
-
-This is a plugin for Redmine to create a glossary that is a list of terms in a project.
-
-To adapt Redmine 4.0(Rails 5.1), reconstruct a glossary plugin from scratch.