docs: slightly buffed (but incomplete) server setup docs

Author: jippi

README.md

@@ -18,6 +18,7 @@
   - [deb, rpm and apk packages](#deb-rpm-and-apk-packages)
   - [go install](#go-install)
 - [Usage](#usage)
+  - [Webhook Server](#webhook-server)
   - [GitLab-CI pipeline](#gitlab-ci-pipeline)
 - [Commands](#commands)
   - [`evaluate`](#evaluate)
@@ -113,9 +114,35 @@ go install github.com/jippi/scm-engine/cmd@latest
 
 ## Usage
 
+### Webhook Server
+
+Using `scm-engine` as a webhook server allows for richer feature set compared to [GitLab CI pipeline](#gitlab-ci-pipeline) mode
+
+- `+` Reacting to comments
+- `+` Access to webhook event data in scripts via `webhook_event.*` (see [server docs](#server) for more information)
+- `+` A single `scm-engine` instance (and single token) for your GitLab project, group, or instance depending on where you configure the webhook.
+- `+` Each Project still have their own `.scm-engine.yml` file, it's downloaded via the API when the server is processing a webhook event.
+- `+` A single "bot" identity across your projects.
+- `+` Turn key once configured; if a project want to use `scm-engine` they just need to create the `.scm-engine.yml` file in their project.
+- `+` Real-time reactions to changes
+- `-` No intuitive access to [`evaluation` logs](#evaluate) within GitLab (you can see them in the server logs or in the webhook failure log)
+
+**Setup**:
+
+1. Deploy `scm-engine` within your infrastructure in an environment that can communicate egress/ingress with GitLab. ([see `server`](#server))
+1. Configure your `webhook` at Project, Group, or Server level to hit the `/gitlab` endpoint on the `scm-engine` server endpoint. ([see `server`](#server))
+
 ### GitLab-CI pipeline
 
-Using scm-engine within a GitLab CI pipeline is straight forward.
+Using `scm-engine` within a GitLab CI pipeline is straight forward - every time a CI pipeline runs, `scm-engine` will [evaluate](#evaluate) the Merge Request.
+
+- `+` Simple & quick installation.
+- `+` Limited access token permissions.
+- `+` Easy access to [`evaluation` logs](#evaluate) within the GitLab CI job.
+- `-` Can't react to comments; only works within a CI pipeline.
+- `-` Higher latency for reacting to changes depending on how fast CI jobs run (and where in the pipeline it runs).
+
+**Setup**:
 
 1. Add a `.scm-engine.yml` file in the root of your project.
 1. Create a [CI/CD Variable](https://docs.gitlab.com/ee/ci/variables/#for-a-group)