Add '.gitattributes' file to make language linguist more descriptive

Author: yasulab

.gitattributes

@@ -0,0 +1,14 @@
+# Example of a `.gitattributes` file which reclassifies `.rb` files as Java:
+#
+#   *.rb linguist-language=Java
+#
+# See: https://github.com/github-linguist/linguist/blob/master/docs/overrides.md
+
+# Mark Jekyll-based markups as Ruby
+_includes/*    linguist-language=Ruby
+_layouts/*     linguist-language=Ruby
+event.html     linguist-language=Ruby
+index.html     linguist-language=Ruby
+session.html   linguist-language=Ruby
+timetable.html linguist-language=Ruby
+workshop.html  linguist-language=Ruby