Add documentation on OSS to EE migration to README (#654)

* ADD documentation on OSS to EE migration to README

* Fix paths in example shell output

MIGRATION.md

@@ -0,0 +1,42 @@
+# Migration
+
+Migrating data from Conjur Open Source to a Conjur EE appliance is simple
+using the provided export tools.
+
+#### Creating a migration archive
+
+To create the migration data archive:
+
+1. Open a shell session in the Conjur Open Source container, for example:
+    ```sh-session
+    $ docker-compose exec conjur bash
+    # OR
+    $ docker exec -it conjur bash
+    ```
+
+2. Run the export command
+    ```sh-session
+    $ conjurctl export -o /var/export
+    Exporting to '/var/export'...
+    Generating key file /var/export/key
+    gpg: directory `/root/.gnupg' created
+    gpg: new configuration file `/root/.gnupg/gpg.conf' created
+    gpg: WARNING: options in `/root/.gnupg/gpg.conf' are not yet active during this run
+    gpg: keyring `/root/.gnupg/pubring.gpg' created
+
+    Export placed in /var/export/2018-07-23T21-08-19Z.tar.xz.gpg
+    It's encrypted with key in /var/export/key.
+    If you're going to store the export, make
+    sure to store the key file separately.
+    ```
+
+3. Copy the data archive and encryption key out of the container
+    > NOTE: There will be two files in the export:
+    > - A file called `key`, which contains the encryption key for the archive
+    > - A timestamped file ending with `.tar.xz.gpg`. This is the exported Conjur
+    >   data, protected by the key
+    ```sh-session
+    $ docker copy conjur:/var/export ./export
+    ```
+
+These files can now be used to migrate the data into a new Conjur EE appliance.

README.md

@@ -38,6 +38,13 @@ _Note: our badges and social media buttons never track you._
 Our primary channel for support is through our Slack community. More
 here: [community support](https://www.conjur.org/support.html)
 
+## Migrating to Conjur EE
+
+Migrating data from Conjur Open Source to Conjur EE is simple using our
+[migration guide][migration]
+
+[migration]: MIGRATION.md
+
 # Development
 
 We welcome contributions of all kinds to Conjur. See our [contributing