Add doc for env --shell option

Signed-off-by: Nathan LeClaire <nathan.leclaire@gmail.com>

docs/index.md

@@ -156,6 +156,7 @@ dev    *        virtualbox   Running   tcp://192.168.99.100:2376
 
 The `*` next to `dev` indicates that it is the active host.
 
+
 Next, as noted in the output of the `docker-machine create` command, we have to tell
 Docker to talk to that machine.  You can do this with the `docker-machine env`
 command.  For example,
@@ -165,6 +166,11 @@ $ eval "$(docker-machine env dev)"
 $ docker ps
 ```
 
+> **Note**: If you are using `fish`, or a Windows shell such as
+> Powershell/`cmd.exe` the above method will not work as described.  Instead,
+> see [the `env` command's documentation](https://docs.docker.com/machine/#env)
+> to learn how to set the environment variables for your shell.
+
 This will set environment variables that the Docker client will read which specify
 the TLS settings. Note that you will need to do that every time you open a new tab or
 restart your machine.
@@ -384,6 +390,7 @@ Load the Machine configuration into your shell:
 ```
 $ eval "$(docker-machine env local)"
 ```
+
 Then run generate the token using the Swarm Docker image:
 
 ```
@@ -574,8 +581,8 @@ Set environment variables to dictate that `docker` should run a command against
 a particular machine.
 
 `docker-machine env machinename` will print out `export` commands which can be
-run in a subshell.  Running `docker-machine env -u` will print
+run in a subshell.  Running `docker-machine env -u` will print `unset` commands
-`unset` commands which reverse this effect.
+which reverse this effect.
 
 ```
 $ env | grep DOCKER
@@ -590,6 +597,47 @@ $ env | grep DOCKER
 $ # The environment variables have been unset.
 ```
 
+The output described above is intended for the shells `bash` and `zsh` (if
+you're not sure which shell you're using, there's a very good possibility that
+it's `bash`).  However, these are not the only shells which Docker Machine
+supports.
+
+If you are using `fish` and the `SHELL` environment variable is correctly set to
+the path where `fish` is located, `docker-machine env name` will print out the
+values in the format which `fish` expects:
+
+```
+set -x DOCKER_TLS_VERIFY 1;
+set -x DOCKER_CERT_PATH "/Users/nathanleclaire/.docker/machine/machines/overlay";
+set -x DOCKER_HOST tcp://192.168.99.102:2376;
+# Run this command to configure your shell: eval (docker-machine env overlay)
+```
+
+If you are on Windows and using Powershell or `cmd.exe`, `docker-machine env`
+cannot detect your shell automatically, but it does have support for these
+shells.  In order to use them, specify which shell you would like to print the
+options for using the `--shell` flag for `docker-machine env`.
+
+For Powershell:
+
+```
+$ docker-machine.exe env --shell powershell dev
+$Env:DOCKER_TLS_VERIFY = "1"
+$Env:DOCKER_HOST = "tcp://192.168.99.101:2376"
+$Env:DOCKER_CERT_PATH = "C:\Users\captain\.docker\machine\machines\dev"
+# Run this command to configure your shell: docker-machine.exe env --shell=powershell | Invoke-Expression
+```
+
+For `cmd.exe`:
+
+```
+$ docker-machine.exe env --shell cmd dev
+set DOCKER_TLS_VERIFY=1
+set DOCKER_HOST=tcp://192.168.99.101:2376
+set DOCKER_CERT_PATH=C:\Users\captain\.docker\machine\machines\dev
+# Run this command to configure your shell: copy and paste the above values into your command prompt
+```
+
 #### inspect
 
 Inspect information about a machine.