Document tar deployment method

[ci skip]

docs/deployment/methods/tar.md

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+# Tarfile Deployment
+
+> New as of 0.4.0
+
+```
+tar:from <app> <url>                           # Loads an app tarball from url
+tar:in <app>                                   # Reads an tarball containing the app from stdin
+```
+
+## Deploying from a tarball
+
+In some cases, it may be useful to deploy an application from a tarball. For instance, if you implemented a non-git based deployment plugin, tarring the generated artifact may be an easier route to interface with the existing dokku infrastructure.
+
+You can place the tarball on an external webserver and deploy via the `tar:from` command.
+
+```shell
+dokku tar:from node-js-app https://dokku.me/releases/node-js-app/v1
+```
+
+As an alternative, a deploy can be trigged from a tarball read from stdin using the `tar:in` command:
+
+```shell
+# run from the generated artifact directory
+tar c . $* | dokku tar:in node-js-app
+```