docs(core): Adds usage to README

- Adds a quick code sample for creating/reading TDFs
- Other fixes

Author: dmihalcik-virtru

README.md

@@ -1,20 +1,69 @@
 # java-sdk
 
-OpenTDF Java SDK
+This repository provides the OpenTDF Java SDK.
+It will be available from maven central as:
 
-### SDK Usage
-The SDK uses the [Bouncy Castle Security library](https://www.bouncycastle.org/).  SDK users may need to register the Bouncy Castle Provider; e.g.:
+```xml
+    <dependency>
+        <groupId>io.opentdf/platform</groupId>
+        <artifactId>sdk</artifactId>
+    </dependency>
+```
+
+
+
+## SDK Usage
+
+### TDF File Creation and Reading
+
+```java
+import io.opentdf.platform.sdk.Config;
+import io.opentdf.platform.sdk.SDK;
+import io.opentdf.platform.sdk.SDKBuilder;
+import io.opentdf.platform.sdk.abac.Policy;
+import java.io.InputStream;
+import java.io.FileInputStream;
+
+public class Example {
+  public static void main(String args[]) {
+    SDK sdk =
+        new SDKBuilder
+            .clientSecret("myClient", "token")
+            .platformEndpoint("https://your.cluster/")
+            .build();
+    // Encrypt a file
+    try (InputStream in = new FileInputStream("input.plaintext")) {
+      Config c = Config.newTDFConfig(Config.withDataAttributes("attr1", "attr2"))
+      new TDF().createTDF(in, System.out, tdfConfig, sdk.getServices().kas());
+    }
+
+    // Decrypt a file
+    try (SeekableByteChannel in =
+          FileChannel.open("input.ciphertext", StandardOpenOption.READ)) {
+        TDF.Reader reader = new TDF().loadTDF(in, sdk.getServices().kas());
+        reader.readPayload(System.out);
+    }
+}
 ```
+
+### Cryptography Library
+
+The SDK uses the [Bouncy Castle Security library](https://www.bouncycastle.org/).  SDK users may need to register the Bouncy Castle Provider; e.g.:
+
+```java
     static{
         Security.addProvider(new BouncyCastleProvider());
     }
 ```
 
 ### Logging
+
 We use [slf4j](https://www.slf4j.org/), without providing a backend. We use log4j2 in our tests.
 
 ### SSL - Untrusted Certificates
+
 Use the SDKBuilder.withSSL... methods to build an SDKBuilder with:
+
 - An SSLFactory: ```sdkBuilder.sslFactory(mySSLFactory)```
 - Directory containing trusted certificates: ```sdkBuilder.sslFactoryFromDirectory(myDirectoryWithCerts)```
 - Java Keystore: ```sdkBuilder.sslFactoryFromKeyStore(keystorepath, keystorePassword)```