Add docs for jsonnet SSD example (#6908)

Loki's jsonnet libs are no longer in `github.com/grafana/jsonnet-libs`
repo this MR fixes that import.
Also adds some docs for utilizing the example.

production/ksonnet/loki-simple-scalable/example/README.md

@@ -0,0 +1,10 @@
+# Loki Simple Scaleable Deployment Example
+
+
+## Usage
+1) Setup Tanka see the [Tanka Installation Docs](../../../../docs/sources/installation/tanka.md).
+2) Next, you'll need to install Jsonnet library for SSD.
+```bash
+jb install github.com/grafana/loki/production/ksonnet/loki-simple-scalable@main
+```
+3) Configure main.jsonnet and `tk apply` :tada:

production/ksonnet/loki-simple-scalable/example/main.jsonnet

@@ -1,5 +1,5 @@
 local k = import 'ksonnet-util/kausal.libsonnet',
-      loki = import 'github.com/grafana/jsonnet-libs/loki-simple-scalable/loki.libsonnet',
+      loki = import 'loki-simple-scalable/loki.libsonnet',
       namespace = 'loki-ssd-jsonnet-libs',
       cluster = 'ssd-jsonnet-libs',
       grpc_listen_port = 9095,