Fix #2898: Clearer warning message for user (2^max_depth > num_leaves) (#3537)

* Fix #2898: Clearer warning message (2^max_depth > num_leaves).

* Update src/io/config.cpp
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

* Update src/io/config.cpp
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

src/io/config.cpp

@@ -317,7 +317,9 @@ void Config::CheckParamConflict() {
     double full_num_leaves = std::pow(2, max_depth);
     if (full_num_leaves > num_leaves
         && num_leaves == kDefaultNumLeaves) {
-      Log::Warning("Accuracy may be bad since you didn't set num_leaves and 2^max_depth > num_leaves");
+      Log::Warning("Accuracy may be bad since you didn't explicitly set num_leaves OR 2^max_depth > num_leaves."
+                   " (num_leaves=%d).",
+                   num_leaves);
     }
 
     if (full_num_leaves < num_leaves) {