Document that it is allowed to assert on dedicated spy calls.

docs/release-source/release/assertions.md

@@ -82,6 +82,8 @@ Passes if provided spies were called in the specified order.
 
 Passes if `spy` was ever called with `obj` as its `this` value.
 
+It's possible to assert on a dedicated spy call: `sinon.assert.calledOn(spy.firstCall, arg1, arg2, ...);`.
+
 
 #### `sinon.assert.alwaysCalledOn(spy, obj)`
 
@@ -92,6 +94,8 @@ Passes if `spy` was always called with `obj` as its `this` value.
 
 Passes if `spy` was called with the provided arguments.
 
+It's possible to assert on a dedicated spy call: `sinon.assert.calledWith(spy.firstCall, arg1, arg2, ...);`.
+
 
 #### `sinon.assert.alwaysCalledWith(spy, arg1, arg2, ...);`
 
@@ -107,6 +111,8 @@ Passes if `spy` was never called with the provided arguments.
 
 Passes if `spy` was called with the provided arguments and no others.
 
+It's possible to assert on a dedicated spy call: `sinon.assert.calledWithExactly(spy.getCall(1), arg1, arg2, ...);`.
+
 
 #### `sinon.assert.alwaysCalledWithExactly(spy, arg1, arg2, ...);`
 
@@ -119,6 +125,8 @@ Passes if `spy` was called with matching arguments.
 
 This behaves the same way as `sinon.assert.calledWith(spy, sinon.match(arg1), sinon.match(arg2), ...)`.
 
+It's possible to assert on a dedicated spy call: `sinon.assert.calledWithMatch(spy.secondCall, arg1, arg2, ...);`.
+
 
 #### `sinon.assert.alwaysCalledWithMatch(spy, arg1, arg2, ...)`
 
@@ -147,6 +155,8 @@ The exception can be a `String` denoting its type, or an actual object.
 
 If only one argument is provided, the assertion passes if `spy` ever threw any exception.
 
+It's possible to assert on a dedicated spy call: `sinon.assert.threw(spy.thirdCall, exception);`.
+
 
 #### `sinon.assert.alwaysThrew(spy, exception);`