README: add newline at end of file

Some text editors (such as vim) automatically add a newline at end of
files.  `git diff` also treats absence of newline at end of file in a
special way.

Add a newline at end of file README.md generated by the template to make
it more convenient to use.

.github/template-cleanup/README.md

@@ -41,4 +41,4 @@ To keep everything working, do not remove `<!-- ... -->` sections.
 Plugin based on the [IntelliJ Platform Plugin Template][template].
 
 [template]: https://github.com/JetBrains/intellij-platform-plugin-template
-[docs:plugin-description]: https://plugins.jetbrains.com/docs/intellij/plugin-user-experience.html#plugin-description-and-presentation
+[docs:plugin-description]: https://plugins.jetbrains.com/docs/intellij/plugin-user-experience.html#plugin-description-and-presentation