Collector documentation (#113)

* Initial draft of collector documentation

* Add docs for all collectors

* Update main README with links to docs

* Fix link syntax

docs/collector-template.md

@@ -0,0 +1,45 @@
+# %name% collector
+
+The %name% collector exposes metrics about ...
+
+Metric name prefix | `%name%`
+Classes             | [`...`](https://msdn.microsoft.com/en-us/library/...)
+Enabled by default? | Yes/No
+
+## Flags
+
+### `--collector....`
+
+Add description...
+
+Example: `--collector....`
+
+## Metrics
+
+Name | Description | Type | Labels
+-----|-------------|------|-------
+`wmi_...` | ... | counter/gauge/histogram/summary | ...
+
+### Example metric
+
+...:
+
+`wmi_...{...} 1`
+
+## Useful queries
+### Add queries...
+
+`...`
+
+## Alerting examples
+### Add alerts...
+
+```yaml
+  - alert: ""
+    expr: ""
+    for: ""
+    labels:
+      urgency: ""
+    annotations:
+      summary: ""
+```