Add initial documentation for IncludeCancellationParameter

Fixes DotNetAnalyzers#44

AsyncUsageAnalyzers.sln

@@ -32,6 +32,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "documentation", "documentat
 	ProjectSection(SolutionItems) = preProject
 		documentation\AvoidAsyncSuffix.md = documentation\AvoidAsyncSuffix.md
 		documentation\AvoidAsyncVoid.md = documentation\AvoidAsyncVoid.md
+		documentation\IncludeCancellationParameter.md = documentation\IncludeCancellationParameter.md
 		documentation\UseAsyncSuffix.md = documentation\UseAsyncSuffix.md
 		documentation\UseConfigureAwait.md = documentation\UseConfigureAwait.md
 	EndProjectSection

documentation/IncludeCancellationParameter.md

@@ -0,0 +1,43 @@
+## IncludeCancellationParameter
+
+<table>
+<tr>
+  <td>TypeName</td>
+  <td>IncludeCancellationParameterAnalyzer</td>
+</tr>
+<tr>
+  <td>CheckId</td>
+  <td>IncludeCancellationParameter</td>
+</tr>
+<tr>
+  <td>Category</td>
+  <td>Usage Rules</td>
+</tr>
+</table>
+
+## Cause
+
+An asynchronous method does not include a `CancellationToken` parameter.
+
+## Rule description
+
+This diagnostic identifies asynchronous methods which do not include a `CancellationToken` parameter in their signature.
+
+## How to fix violations
+
+To fix a violation of this rule, add a `CancellationToken` parameter to the signature of the method.
+
+## How to suppress violations
+
+```csharp
+[SuppressMessage("AsyncUsage.CSharp.Usage", "IncludeCancellationParameter", Justification = "Reviewed.")]
+```
+
+```csharp
+#pragma warning disable IncludeCancellationParameter // Include CancellationToken parameter
+public Task<int> ThisMethodCannotBeCancelled()
+#pragma warning restore IncludeCancellationParameter // Include CancellationToken parameter
+{
+    return Task.FromResult(0);
+}
+```