syz-cluster: update README

Include more details about the system.

Author: a-nogikh

syz-cluster/README.md

@@ -1,3 +1,40 @@
+`syz-cluster` is a distributed patch series fuzzing that is relying on syzkaller.
+It's deployed at https://ci.syzbot.org.
+
+## Overview
+
+The system is to be deployed on a K8S cluster. The main services are:
+* `dashboard`: the web interface, read-only.
+* `controller`: manages the state of the system, provides
+  [API](./pkg/api/client.go) for other components, schedules fuzzing sessions.
+* `series-tracker`: polls LKML git archives for the new series.
+* `reporter-server`: generates new reports, provides API for actual reporter
+  implementations.
+* `email-reporter`: sends reports over email, handles incoming email commands.
+
+The actual patch processing is orchestrated by Argo Workflows: see [the
+template](./pkg/workflow/template.yaml). It relies on the following processing
+steps:
+* `workflow/triage-step`
+* `workflow/build-step`
+* `workflow/boot-step`
+* `workflow/fuzz-step`
+
+Triage and build steps need the actual kernel checkouts. The base kernel repo is
+hosted on a shared network disk and is regularly updated by the scripts in
+`kernel-disk`.
+
+The system can be deployed in multiple environments, which is achieved with the
+help of Kustomize. Depending on the actual deployment target, different pieces of
+configuration are applied:
+* `overlays/minikube`: the local dev environment.
+* `overlays/gke/staging`: the staging prod environment.
+* `overlays/gke/prod`: https://ci.syzbot.org.
+
+`global-config.yaml` is the main configuration file of the system - it
+determines the mailing lists to poll, configures resource usage and the actual
+reporting.
+
 ## Local installation steps
 
 1. Install and start minikube: https://minikube.sigs.k8s.io/docs/start/
@@ -26,11 +63,14 @@ $ make k8s-config-argo-wait
 $ make k8s-config-dev | kubectl apply -f -
 $ make migrate-job.yaml | kubectl create -f -
 ```
-5. (Optional) Pre-fetch the kernel git repository:
+5. Pre-fetch the kernel git repository:
 ```
 $ make fetch-kernels-once.yaml | kubectl create -f -
 ```
 
+Note that actual series processing won't start until the job created in (5)
+finishes.
+
 ## Developmental tips
 
 1. Install Argo Workflows client: https://github.com/argoproj/argo-workflows/releases