docs: Add instructions for configuring request logging

Signed-off-by: Philip Gough <philip.p.gough@gmail.com>

docs/logging.md

@@ -0,0 +1,75 @@
+# Logging
+
+Thanos supports query logging via flags.
+
+Components are configured using `--request.logging-config-file` to reference to the configuration file or `--request.logging-config` as YAML directly.
+
+## Configuration
+
+Configuration can be supplied for either gRPC, HTTP or both. Options can be supplied globally, which is applied to both gRPC and HTTP, or individually to either or both protocols.
+
+### HTTP
+
+```yaml
+http:
+  config:
+    - path: /api/v1/query
+      port: 10904
+    - path: /api/v1/app_range/metrics
+      port: 3456
+```
+
+### gRPC
+
+```yaml
+grpc:
+  config:
+    - service: thanos.Store
+      method: Info
+```
+
+### Options
+
+Valid `level` for `options` should be one of `INFO`, `WARNING`, `ERROR` or `DEBUG`.
+
+```yaml
+options:
+  level: ERROR
+  decision:
+    log_start: true
+    log_end: true
+```
+
+## How to use `config` flags?
+
+The following example shows how the logging config can be supplied to the `sidecar` component:
+
+```yaml
+      - args:
+        - sidecar
+        - |
+          --objstore.config=type: GCS
+          config:
+            bucket: <bucket>
+        - --prometheus.url=http://localhost:9090
+        - |
+          --request.logging-config=http:
+            config:
+              - path: /api/v1/query
+                port: 10904
+            options:
+              level: INFO
+              decision:
+                log_start: true
+                log_end: true
+          grpc:
+            config:
+              - service: thanos.Store
+                method: Info
+            options:
+              level: ERROR
+              decision:
+                log_start: true
+                log_end: true          
+        - --tsdb.path=/prometheus-data
+```