docs(README): Add non-GCP instructions to README

1 files changed, 33 insertions, 9 deletions

diff --git a/README.md b/README.md
index 0ed149fb8f..28b72b9872 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,20 @@ directly to a Google Compute Engine instance and will use the
 [metadata server][] to figure out credentials and instance
 identification.
 
-## Usage
+## Features
+
+* `journaldriver` persists the last forwarded position in the journal
+  and will resume forwarding at the same position after a restart
+* `journaldriver` will recognise log entries in JSON format and
+  forward them appropriately to make structured log entries available
+  in Stackdriver
+* `journaldriver` can be used outside of GCP by configuring static
+  credentials
+
+## Usage on Google Cloud Platform
+
+`journaldriver` does not require any configuration when running on GCP
+instances.
 
 1. Install `journaldriver` on the instance from which you wish to
    forward logs.
@@ -26,19 +39,30 @@ identification.
    By default instances have the required permissions if Stackdriver
    Logging support is enabled in the project.
 
-3. Start Stackdriver, for example via `systemd`.
+3. Start `journaldriver`, for example via `systemd`.
+
+
+## Usage outside of Google Cloud Platform
+
+When running outside of GCP, the following extra steps need to be
+performed:
+
+1. Create a Google Cloud Platform service account with the "Log
+   Writer" role and download its private key in JSON-format.
+2. When starting `journaldriver`, configure the following environment
+   variables:
+
+   * `GOOGLE_CLOUD_PROJECT`: Name of the GCP project to which logs
+     should be written.
+   * `GOOGLE_APPLICATION_CREDENTIALS`: Filesystem path to the
+     JSON-file containing the service account's private key.
+   * `LOG_NAME`: Name of the target log stream in Stackdriver Logging.
+     This will be automatically created if it does not yet exist.
 
 ## Upcoming features:
 
 * `journaldriver` will be added to [nixpkgs][] with a complementary
   [NixOS][] module for easy configuration.
-* `journaldriver` will persist the latest `journald` cursor position,
-  allowing log reads to resume from the same position where they
-  stopped after a restart
-* `journaldriver` will attempt to figure out whether logs are in
-  JSON-format and use the coresponding `jsonPayload` field in
-  Stackdriver Logging to make structured logs easily accessible
-* `journaldriver` will support deployments on non-GCP machines
 
 [Stackdriver Logging]: https://cloud.google.com/logging/
 [metadata server]: https://cloud.google.com/compute/docs/storing-retrieving-metadata