add documentation for system gc endpoint and update log docs

website/source/docs/http/system.html.md

@@ -0,0 +1,38 @@
+---
+layout: "http"
+page_title: "HTTP API: /v1/system/"
+sidebar_current: "docs-http-system"
+description: |-
+  The '/1/system/' endpoints are used to for system maintance.
+---
+
+# /v1/system
+
+The `system` endpoint is used to for system maintance and should not be
+necessary for most users. By default, the agent's local region is used; another
+region can be specified using the `?region=` query parameter.
+
+## PUT
+
+<dl>
+  <dt>Description</dt>
+  <dd>
+    Initiate garbage collection of jobs, evals, allocations and nodes.
+  </dd>
+
+  <dt>Method</dt>
+  <dd>GET</dd>
+
+  <dt>URL</dt>
+  <dd>`/v1/system/gc`</dd>
+
+  <dt>Parameters</dt>
+  <dd>
+    None
+  </dd>
+
+  <dt>Returns</dt>
+  <dd>
+    None
+  </dd>
+</dl>