Add missing Java SDK anchor (#144)

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

Author: tzolov

docs.json

@@ -86,6 +86,11 @@
           "href": "https://github.com/modelcontextprotocol/typescript-sdk",
           "icon": "square-js"
         },
+        {
+          "anchor": "Java SDK",
+          "href": "https://github.com/modelcontextprotocol/java-sdk",
+          "icon": "java"
+        },
         {
           "anchor": "Kotlin SDK",
           "href": "https://github.com/modelcontextprotocol/kotlin-sdk",