[siemensrds] Update to documentation (#13913)

* [siemensrds] resolve issue #13906
* [siemensrds] add chapter to readme

Signed-off-by: Andrew Fiddian-Green <software@whitebear.ch>

bundles/org.openhab.binding.siemensrds/src/main/java/org/openhab/binding/siemensrds/internal/RdsAccessToken.java

@@ -27,6 +27,7 @@ import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.util.Calendar;
 import java.util.Date;
+import java.util.Locale;
 
 import javax.net.ssl.HttpsURLConnection;
 
@@ -61,7 +62,7 @@ public class RdsAccessToken {
 
     private @Nullable Date expDate = null;
 
-    /*
+    /**
      * public static method: execute the HTTP POST on the server
      */
     public static String httpGetTokenJson(String apiKey, String payload) throws RdsCloudException, IOException {
@@ -105,14 +106,14 @@ public class RdsAccessToken {
         }
     }
 
-    /*
+    /**
      * public method: parse the JSON, and create a class that encapsulates the data
      */
     public static @Nullable RdsAccessToken createFromJson(String json) {
         return GSON.fromJson(json, RdsAccessToken.class);
     }
 
-    /*
+    /**
      * public method: return the access token
      */
     public String getToken() throws RdsCloudException {
@@ -123,14 +124,14 @@ public class RdsAccessToken {
         throw new RdsCloudException("no access token");
     }
 
-    /*
+    /**
      * public method: check if the token has expired
      */
     public boolean isExpired() {
         Date expDate = this.expDate;
         if (expDate == null) {
             try {
-                expDate = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss z").parse(expires);
+                expDate = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss z", Locale.ENGLISH).parse(expires);
             } catch (ParseException e) {
                 logger.debug("isExpired: expiry date parsing exception");