Add javadoc (#5329)

Signed-off-by: Fabio Di Fabio <fabio.difabio@consensys.net>

util/src/main/java/org/hyperledger/besu/util/platform/PlatformDetector.java

@@ -104,6 +104,12 @@ public class PlatformDetector {
     return _glibc;
   }
 
+  /**
+   * Gets jemalloc version.
+   *
+   * @throws UnsatisfiedLinkError if the library cannot be found or dependent libraries are missing.
+   * @return the jemalloc version
+   */
   public static String getJemalloc() {
     if (_jemalloc == null) {
       detectJemalloc();