Add a readme (#2)

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README.md

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+# AccessibilityTextSnapshot
+
+A [snapshot strategy](https://github.com/pointfreeco/swift-snapshot-testing#snapshot-anything) for testing your VoiceOvers support in UIKit, using the [SnapshotTesting](https://github.com/pointfreeco/swift-snapshot-testing) library by PointFree.
+
+This strategy uses a _textual_ representation of the view hierarchy, focusing on just the information that is relevant for VoiceOver. (Related work: [AccessibilitySnapshot](https://github.com/cashapp/AccessibilitySnapshot) is a _visual_ snapshot-test tool for a similar use case.)
+
+## Usage
+
+    import SnapshotTesting
+    import AccessibilityTextSnapshot
+
+    assertSnapshot(                     // SnapshotTesting gives you this...
+        matching: someView,
+        as: .recursiveA11yDescription)  // ... but AccessibilityTextSnapshot gives you this
+
+This generates a recursive (textual) description of all voiceover-relevant information, suitable for snapshot testing.
+
+The string shows
+* all UIView subclasses with isAccessibilityElement true, together with their ancestor UIViews (if any) to show hierarchy
+* their voiceover-relevant properties (accessibilityValue, accessibilityLabel, etc) 
+* any a11y-relevant *sub*views they might have, prefixed by `| ` to emphasise that they are *not* involved in VoiceOver
+
+It does *not* show UIImageViews, which we maybe should reconsider at some point.
+
+Example:
+
+    * UIView                                       // non-a11y view but has a11y-relevant descendant
+       * UIScrollView                              // (same)
+         * UIView                                  // (same)
+           * UIStackView                           // ...
+             * MDViewLayer.ElementView
+               * UIStackView
+                 * MDViewModels.Label              // | hanging from this view means it has a11y-relevant stuff
+                 | -label: Relaxation exercises    // a11y property
+                 | -traits: .staticText            // a11y property
+                 * UIStackView
+                   * MDViewLayer.MultilineButton
+                   | -label: Yes
+                   | -hint: Unselected option
+                   | -traits: .button
+                   * MDViewLayer.MultilineButton
+                   | -label: No
+                   | -hint: Unselected option
+                   | -traits: .button
+             * MDViewLayer.ConversationListItemView // hanging | means a11y-relevant view
+             | -label: Only you. No messages yet    // a11y property
+             | -hint: Open conversation             // a11y property
+             | * UIStackView                        // subviews that would be a11y-relevant
+             |   * UIStackView                      // BUT are not read by VoiceOver because
+             |     * UIStackView                    // the parent view overrides, note leading |
+             |       * MDViewModels.Label
+             |       | -label: Only you
+             |     * UIStackView
+             |       * MDViewModels.Label
+             |       | -label: No messages yet.
+             |   * MDViewLayer.Button
+             |     * UIView
+             |       * MDViewModels.Label
+             |       | -label: Ongoing video call
+             o MDViewLayer.StepValidationView        // o means isHidden=true (on self or a parent)
+             o -label: Please correct the errors above. Actions available
+             o -action: Go to first error            // We still show it because we want to
+             o * MDViewLayer.MultilineButton         // be reminded that there *could* be something!
+             o | -label: Please correct the errors above
+
+
+
+## Installing with CocoaPods
+
+    target 'MyAppTests' do
+      pod 'AccessibilityTextSnapshot'
+    end
+