Add newlines styleguide for Ruby code

CONTRIBUTING.md

@@ -459,6 +459,7 @@ merge request:
     - multi-line method chaining style **Option B**: dot `.` on previous line
     - string literal quoting style **Option A**: single quoted by default
 1.  [Rails](https://github.com/bbatsov/rails-style-guide)
+1.  [Newlines styleguide][newlines-styleguide]
 1.  [Testing](doc/development/testing.md)
 1.  [CoffeeScript](https://github.com/thoughtbot/guides/tree/master/style/coffeescript)
 1.  [SCSS styleguide][scss-styleguide]
@@ -530,6 +531,7 @@ available at [http://contributor-covenant.org/version/1/1/0/](http://contributor
 [rss-naming]: https://github.com/bbatsov/ruby-style-guide/blob/master/README.md#naming
 [doc-styleguide]: doc/development/doc_styleguide.md "Documentation styleguide"
 [scss-styleguide]: doc/development/scss_styleguide.md "SCSS styleguide"
+[newlines-styleguide]: doc/development/newlines_styleguide.md "Newlines styleguide"
 [gitlab-design]: https://gitlab.com/gitlab-org/gitlab-design
 [free Antetype viewer (Mac OSX only)]: https://itunes.apple.com/us/app/antetype-viewer/id824152298?mt=12
 [`gitlab8.atype` file]: https://gitlab.com/gitlab-org/gitlab-design/tree/master/current/

doc/development/newlines_styleguide.md

+# Newlines styleguide
+
+This style guide recommends best practices for newlines in Ruby code.
+
+## Rule: separate code with newlines only when it makes sense from logic perspectice
+
+```ruby
+# bad
+def method
+  issue = Issue.new
+
+  issue.save
+  
+  render json: issue 
+end
+```
+
+```ruby
+# good
+def method
+  issue = Issue.new
+  issue.save
+  
+  render json: issue 
+end
+```
+
+## Rule: separate code and block with newlines
+
+### Newline before block
+
+```ruby
+# bad
+def method
+  issue = Issue.new
+  if issue.save
+    render json: issue
+  end
+end
+```
+
+```ruby
+# good
+def method
+  issue = Issue.new
+
+  if issue.save
+    render json: issue
+  end
+end
+```
+
+## Newline after block
+
+```ruby
+# bad
+def method
+  if issue.save
+    issue.send_email
+  end
+  render json: issue
+end
+```
+
+```ruby
+# good
+def method
+  if issue.save
+    issue.send_email
+  end
+
+  render json: issue
+end
+```
+
+### Exception: no need for newline when code block starts or ends right inside another code block
+
+```ruby
+# bad
+def method
+
+  if issue
+
+    if issue.valid?
+      issue.save
+    end
+
+  end
+
+end
+```
+
+```ruby
+# good
+def method
+  if issue
+    if issue.valid?
+      issue.save
+    end
+  end
+end
+```