feat(CI): add a GitHub Action to lint the Markdown

Run on pull request only
Using https://www.npmjs.com/package/markdownlint-cli
Lint Markdown for rules:
- MD009/no-trailing-spaces
- MD012/no-multiple-blanks
- MD022/blanks-around-headings
- MD031/blanks-around-fences
- MD032/blanks-around-lists

1 files changed, 15 insertions, 13 deletions

diff --git a/mrbgems/mruby-io/README.md b/mrbgems/mruby-io/README.md
index 51bdbe014..db52c4a74 100644
--- a/mrbgems/mruby-io/README.md
+++ b/mrbgems/mruby-io/README.md
@@ -4,6 +4,7 @@ mruby-io
 `IO` and `File` classes for mruby
 
 ## Installation
+
 Add the line below to your build configuration.
 
 ```
@@ -13,6 +14,7 @@ Add the line below to your build configuration.
 ## Implemented methods
 
 ### IO
+
  - https://doc.ruby-lang.org/ja/1.9.3/class/IO.html
 
 | method                     | mruby-io | memo |
@@ -97,6 +99,7 @@ Add the line below to your build configuration.
 | IO#write_nonblock          |          |      |
 
 ### File
+
  - https://doc.ruby-lang.org/ja/1.9.3/class/File.html
 
 | method                      | mruby-io | memo |
@@ -167,26 +170,25 @@ Add the line below to your build configuration.
 | File#size                   |          |      |
 | File#truncate               |          |      |
 
-
 ## License
 
 Copyright (c) 2013 Internet Initiative Japan Inc.
 Copyright (c) 2017 mruby developers
 
-Permission is hereby granted, free of charge, to any person obtaining a 
-copy of this software and associated documentation files (the "Software"), 
-to deal in the Software without restriction, including without limitation 
-the rights to use, copy, modify, merge, publish, distribute, sublicense, 
-and/or sell copies of the Software, and to permit persons to whom the 
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of this software and associated documentation files (the "Software"),
+to deal in the Software without restriction, including without limitation
+the rights to use, copy, modify, merge, publish, distribute, sublicense,
+and/or sell copies of the Software, and to permit persons to whom the
 Software is furnished to do so, subject to the following conditions:
 
-The above copyright notice and this permission notice shall be included in 
+The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.
 
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 
-FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 DEALINGS IN THE SOFTWARE.