Add link pointing to a new notebook (#347)

* Add link pointing to a new notebook

* Add test

lib/livebook/notebook/explore/distributed_portals_with_elixir.livemd

@@ -695,7 +695,7 @@ Now we have everything we need to connect across notebooks.
 
 ### Notebook connections
 
-In order to connect across notebooks, open up a new empty notebook
+In order to connect across notebooks, open up [a new empty notebook](/explore/notebooks/new)
 in a separate tab, copy and paste the code below to this new notebook,
 and execute it:
 

lib/livebook/notebook/explore/vm_introspection.livemd

@@ -30,7 +30,7 @@ inside it. This will also give you a better idea of how you can
 inspect a remote node in general.
 
 The first thing we need is a separate Elixir node. For this example,
-you can do so by opening up a new notebook, since Livebook
+you can do so by opening up [a new notebook](/explore/notebooks/new), since Livebook
 automatically starts each notebook as a remote node.
 
 In practice, you may want to start an existing Elixir system,

lib/livebook_web/live/explore_live.ex

@@ -91,6 +91,10 @@ defmodule LivebookWeb.ExploreLive do
   end
 
   @impl true
+  def handle_params(%{"slug" => "new"}, _url, socket) do
+    {:noreply, create_session(socket)}
+  end
+
   def handle_params(%{"slug" => slug}, _url, socket) do
     {notebook, images} = Explore.notebook_by_slug!(slug)
     {:noreply, create_session(socket, notebook: notebook, images: images)}

test/livebook_web/live/explore_live_test.exs

@@ -16,4 +16,13 @@ defmodule LivebookWeb.ExploreLiveTest do
     {:ok, view, _} = live(conn, to)
     assert render(view) =~ "Welcome to Livebook"
   end
+
+  test "link to a new notebook creates an empty session", %{conn: conn} do
+    {:ok, view, _} =
+      conn
+      |> live("/explore/notebooks/new")
+      |> follow_redirect(conn)
+
+    assert render(view) =~ "Untitled notebook"
+  end
 end