Added DeepL plan link

app/src/main/java/eu/faircode/email/DeepL.java

@@ -68,6 +68,7 @@ public class DeepL {
     private static JSONArray jlanguages = null;
 
     private static final int DEEPL_TIMEOUT = 20; // seconds
+    private static final String PLAN_URI = "https://www.deepl.com/pro-account/plan";
     private static final String PRIVACY_URI = "https://www.deepl.com/privacy/";
 
     // curl https://api-free.deepl.com/v2/languages \
@@ -329,6 +330,13 @@ public class DeepL {
                 }
             });
 
+            tvUsage.setOnClickListener(new View.OnClickListener() {
+                @Override
+                public void onClick(View view) {
+                    Helper.view(view.getContext(), Uri.parse(PLAN_URI), true);
+                }
+            });
+
             tvPrivacy.setPaintFlags(tvPrivacy.getPaintFlags() | Paint.UNDERLINE_TEXT_FLAG);
             tvPrivacy.setOnClickListener(new View.OnClickListener() {
                 @Override