re-doing Docker Engine overview topics for v.1.12

fixed broken links created from Engine Overview update by adding missing topic to daemon reference page and updating the hrefs in the api pages

Signed-off-by: Victoria Bialas <victoria.bialas@docker.com>

docs/reference/commandline/dockerd.md

@@ -139,6 +139,68 @@ The Docker client will honor the `HTTP_PROXY`, `HTTPS_PROXY`, and `NO_PROXY`
 environment variables (or the lowercase versions thereof). `HTTPS_PROXY` takes
 precedence over `HTTP_PROXY`.
 
+### Bind Docker to another host/port or a Unix socket
+
+> **Warning**:
+> Changing the default `docker` daemon binding to a
+> TCP port or Unix *docker* user group will increase your security risks
+> by allowing non-root users to gain *root* access on the host. Make sure
+> you control access to `docker`. If you are binding
+> to a TCP port, anyone with access to that port has full Docker access;
+> so it is not advisable on an open network.
+
+With `-H` it is possible to make the Docker daemon to listen on a
+specific IP and port. By default, it will listen on
+`unix:///var/run/docker.sock` to allow only local connections by the
+*root* user. You *could* set it to `0.0.0.0:2375` or a specific host IP
+to give access to everybody, but that is **not recommended** because
+then it is trivial for someone to gain root access to the host where the
+daemon is running.
+
+Similarly, the Docker client can use `-H` to connect to a custom port.
+The Docker client will default to connecting to `unix:///var/run/docker.sock`
+on Linux, and `tcp://127.0.0.1:2376` on Windows.
+
+`-H` accepts host and port assignment in the following format:
+
+    tcp://[host]:[port][path] or unix://path
+
+For example:
+
+-   `tcp://` -> TCP connection to `127.0.0.1` on either port `2376` when TLS encryption
+    is on, or port `2375` when communication is in plain text.
+-   `tcp://host:2375` -> TCP connection on
+    host:2375
+-   `tcp://host:2375/path` -> TCP connection on
+    host:2375 and prepend path to all requests
+-   `unix://path/to/socket` -> Unix socket located
+    at `path/to/socket`
+
+`-H`, when empty, will default to the same value as
+when no `-H` was passed in.
+
+`-H` also accepts short form for TCP bindings:
+
+    `host:` or `host:port` or `:port`
+
+Run Docker in daemon mode:
+
+    $ sudo <path to>/dockerd -H 0.0.0.0:5555 &
+
+Download an `ubuntu` image:
+
+    $ docker -H :5555 pull ubuntu
+
+You can use multiple `-H`, for example, if you want to listen on both
+TCP and a Unix socket
+
+    # Run docker in daemon mode
+    $ sudo <path to>/dockerd -H tcp://127.0.0.1:2375 -H unix:///var/run/docker.sock &
+    # Download an ubuntu image, use default Unix socket
+    $ docker pull ubuntu
+    # OR use the TCP port
+    $ docker -H tcp://127.0.0.1:2375 pull ubuntu
+
 ### Daemon storage-driver option
 
 The Docker daemon has support for several different image layer storage