Update README

Author: philptr

README.md

@@ -16,6 +16,33 @@ This repo is an experiment on designing and implementing a cross-platform SwiftU
 
 A `PredicateView` can be initialized using a binding to a [`Predicate`](https://developer.apple.com/documentation/foundation/predicate) and a collection of row templates. Note: it purposefully uses the same terminology for row templates as `NSPredicateEditor`.
 
+`PredicateView` has built-in support for common primitive and compound Swift types, including `Bool`, `String`, `Numeric`, `CaseIterable`, and `RawRepresentable`. It uses appropriate customized UI controls for each one, such as menus for enums, segmented controls for booleans, and steppers for numeric data.
+
+You construct a `PredicateView` by providing a `Binding` to a `Predicate` over your model type. You then provide a collection of row templates, which define the set of properties the user will be able to filter through. Each template must contain a `KeyPath` in your model type, as well as a user-friendly title. 
+
+As the user makes changes to the predicate using the `PredicateView` UI, the value of the predicate will update. If your model instance conforms to `Sequence`, you can easily filter it using the predicate by calling the Swift standard library `filter(_:)` method. Note that it is a good practice to opt into updating the filtered-down representation of the model live as the user interacts with the `PredicateView` UI, instead of requiring the user to interact with an additional control, such as an explicit Search button.
+
+### Optionals
+
+`PredicateView` has built-in support for optionals of all supported types. If a given row template uses an optional `KeyPath`, the user will be able to filter over the existence or non-existence of values, in addition to the values themselves.
+
+### Collections
+
+You can provide nested row templates for `Collection` backed data, which will allow the user to customize their query even more, filtering over containment or filtering elements that satisfy all of the conditions.
+
+```swift
+.init(keyPath: \.preferredColors, title: "Preferred Colors", rowTemplates: [
+    .init(keyPath: \.name, title: "Name"),
+    .init(keyPath: \.cost, title: "Cost"),
+]),
+```
+
+![Collections Menu](Resources/CollectionsMenu.png "User-facing Collections Menu")
+
+### Sample Code
+
+See the built-in `PredicateDemoView` for a complete sample use case.
+
 ```swift
 /// A sample model type.
 struct Model: Identifiable {
@@ -42,16 +69,19 @@ PredicateView(predicate: $predicate, rowTemplates: [
     .init(keyPath: \.firstName, title: "First Name"),
     .init(keyPath: \.age, title: "Age"),
     .init(keyPath: \.employmentStatus, title: "Employment Status"),
-    .init(keyPath: \.isRegistered, title: "Registration Status")
+    .init(keyPath: \.isRegistered, title: "Registration Status"),
+    .init(keyPath: \.preferredColors, title: "Preferred Colors", rowTemplates: [
+        .init(keyPath: \.name, title: "Name"),
+        .init(keyPath: \.cost, title: "Cost"),
+    ]),
 ])
 ```
 
-See the built-in `PredicateDemoView` for a complete sample use case.
-
 ## Features
 
 - [x] Easy setup
 - [x] Type safety
+- [x] Built-in support for optionals and nested expressions
 - [x] Rich representations for supported data types
 
 ## Not Features