Update docs

doc/frontend/README.md

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 - [Backbone with organizations](doc/frontend/js/backbone-with-organizations.md)
 - [Global objects](doc/frontend/js/global-objects.md)
-- [Conventions](doc/frontend/conventions)
+- [Conventions](doc/frontend/js/conventions.md)
+- [URLs](doc/frontend/urls.md)

doc/frontend/urls.md

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+URLs within the application might be necessary.
+
+To avoid constructing these URLS manually, i.e. concatenating strings and thus duplicating logic, there are convenient ways of constructing them. Depending on context (server- or client-side) you might take one approach or another.
+
+## Rails
+In Rails simply use the [standard routing helper methods](http://guides.rubyonrails.org/v3.2.21/routing.html). Have a look at  [routes.rb](https://github.com/CartoDB/cartodb/blob/master/config/routes.rb) for the semantic names and paths available.
+
+## Client-side
+For a current sub-app you can access URLs through the current router model, e.g. `router.currentUrl()`.
+
+For a URL that is associated with a specific model you can access the URL by call `.viewUrl()` on that model, and chaining methods afterwards to "drill down" on what (available) path you want, e.g.
+- `user.viewUrl().dashboard().datasets())`, the URL to a user's datasets on the dashboard.
+- `vis.viewUrl().public()`, the URL to a visualization's public page.
+
+See the [models](https://github.com/CartoDB/cartodb/blob/master/lib/assets/test/spec/cartodb/common/urls) for available models and methods.