add observable dictionary docs page

docs/articles/collections-dict.md

@@ -1,3 +1,44 @@
 # Observable Dictionary
 
-> TODO: document
+`ObservableDictionary<T>` is an observable wrapper around the standard `Dictionary<T>`, providing the same API for managing the collection.
+
+In addition to the standard dictionary methods, it provides the [`Observe`](xref:TinkState.ObservableDictionary`2.Observe) method to expose itself as a read-only observable so one can bind to it and react to its changes.
+
+```csharp
+interface ObservableDictionary<TKey, TValue> : IDictionary<TKey, TValue>
+{
+	Observable<IReadOnlyDictionary<TKey, TValue>> Observe();
+}
+```
+
+Like most of observables, `ObservableDictionary<T>` can be created by a static function in the `Observable` helper class:
+
+```csharp
+static class Observable
+{
+	static ObservableDictionary<TKey, TValue> Dictionary<TKey, TValue>();
+}
+```
+
+Adding and removing items will naturally trigger its bindings and propagate through auto-observables.
+
+## Example
+
+```csharp
+var dict = Observable.Dictionary<string, int>();
+dict["a"] = 1;
+dict["b"] = 2;
+
+var auto = Observable.Auto(() => string.Join(",", dict.Select(kvp => $"{kvp.Key}:{kvp.Value}")));
+Console.WriteLine(auto.Value); // a:1,b:2
+
+// initial binding prints a:1 and b:2
+dict.Observe().Bind(readOnlyDict =>
+{
+	foreach (var (key, value) in readOnlyDict) Console.WriteLine($"{key}:{value}");
+});
+
+dict["c"] = 3; // binding prints a:1, b:2 and c:3
+
+Console.WriteLine(auto.Value); // a:1,b:2,c:3
+```

docs/articles/collections-list.md

@@ -2,7 +2,7 @@
 
 `ObservableList<T>` is an observable wrapper around the standard `List<T>`, providing the same API for managing the collection.
 
-In addition to the standard list method, it provides the [`Observe`](xref:TinkState.ObservableList`1.Observe) method to expose itself
+In addition to the standard list methods, it provides the [`Observe`](xref:TinkState.ObservableList`1.Observe) method to expose itself
 as a read-only observable so one can bind to it and react to its changes.
 
 ```csharp