docs: add basic usage

README.md

@@ -6,6 +6,49 @@ High-level, trimmer- and AOT-friendly bindings for the [D-Bus Secret Service API
 
 The bindings target .NET 6.0.
 
-## Usage
+## Basic Usage
 
-**WIP**
+```csharp
+// Connect to the D-Bus Secret Service API
+// Sessions can use either plaintext or encrypted transport
+SecretService secretService = await SecretService.ConnectAsync(EncryptionType.Dh);  // DH Key Agreement for Encryption
+
+// Items are stored in within collections
+// Collections can be retrieved using their alias
+// Note that collection retrieval can fail, so this would need to be handled
+Collection? defaultCollection = await secretService.GetDefaultCollectionAsync();
+if (defaultCollection == null)
+{
+    // ... handle case where collection is not found
+}
+
+// Items are created with the following:
+// - Label - The displayed label in e.g. GNOME Keyring, KWallet etc.
+// - Lookup Attributes - These are used to search for the item later
+// - Secret - The secret value as a byte array
+// - Content Type - A content type hint for the secret value
+string itemLabel = "MySecretValue";
+Dictionary<string, string> lookupAttributes = new()
+{
+    { "my-lookup-attribute", "my-lookup-attribute-value" }
+};
+
+byte[] secretValue = Encoding.UTF8.GetBytes("my secret value");
+string contentType = "text/plain; charset=utf8";
+
+// Note that item creation can fail, e.g. if the collection could not be unlocked
+Item? createdItem = await defaultCollection.CreateItemAsync(label, lookupAttributes, secretBytes, contentType, true);
+if (createdItem == null)
+{
+    // ... handle case where item creation failed
+}
+
+// Later, if we want to retrieve this secret value, we need to search using the same lookup attributes
+// Note that it's possible for multiple items to match the provided lookup attributes
+Item[] matchedItems = await defaultCollection.SearchItemsAsync(lookupAttributes);
+foreach (Item matchedItem in matchedItems)
+{
+    byte[] matchedSecret = await item.GetSecretAsync();
+    string matchedSecretString = Encoding.UTF8.GetString(secret);   // my secret value
+}
+```