surfacing Learn by example topics to top level of Docker Engine docs

fixing links after moving surfacing tutorials

fixing more links for the newly located tutorials

WIP: merging 3 getting started tutorials into one to cover all platforms, added new files

fixing broken images and links in 3-in-1 getting started, re-wrote story flow, linked to Toolbox, d4mac,d4win

Signed-off-by: Victoria Bialas <victoria.bialas@docker.com>
Upstream-commit: 0254c12e1e0be7a93e3b28e61586ac66168a9b7c
Component: engine

components/engine/docs/getstarted/linux_install_help.md

@@ -0,0 +1,44 @@
+<!--[metadata]>
++++
+aliases = ["/mac/started/"]
+title = "Install Docker and run hello-world"
+description = "Getting started with Docker"
+keywords = ["beginner, getting started, Docker, install"]
+identifier = "getstart_linux_install"
+parent = "getstart_all"
+weight="-80"
++++
+<![end-metadata]-->
+
+# Example: Install Docker on Ubuntu Linux
+
+This installation procedure for users who are unfamiliar with package
+managers, and just want to try out the Getting Started tutorial while running Docker on Linux. If you are comfortable with package managers, prefer not to use
+`curl`, or have problems installing and want to troubleshoot, please use our
+`apt` and `yum` <a href="https://docs.docker.com/engine/installation/"
+target="_blank">repositories instead for your installation</a>.
+
+1. Log into your Ubuntu installation as a user with `sudo` privileges.
+
+2. Verify that you have `curl` installed.
+
+        $ which curl
+
+    If `curl` isn't installed, install it after updating your manager:
+
+        $ sudo apt-get update
+        $ sudo apt-get install curl
+
+3. Get the latest Docker package.
+
+        $ curl -fsSL https://get.docker.com/ | sh
+
+    The system prompts you for your `sudo` password. Then, it downloads and
+    installs Docker and its dependencies.
+
+    >**Note**: If your company is behind a filtering proxy, you may find that the
+    >`apt-key`
+    >command fails for the Docker repo during installation. To work around this,
+    >add the key directly using the following:
+    >
+    >       $ curl -fsSL https://get.docker.com/gpg | sudo apt-key add -