Added Zeroing::offset_ready() helper and TODO.

Change-Id: I1bd1d0e667bb9081896f6f48030b8fcfb95cdc79
diff --git a/frc971/zeroing/zeroing.h b/frc971/zeroing/zeroing.h
index 4176f48..433745a 100644
--- a/frc971/zeroing/zeroing.h
+++ b/frc971/zeroing/zeroing.h
@@ -63,6 +63,11 @@
     return start_pos_samples_.size() / static_cast<double>(max_sample_count_);
   }
 
+  // Returns true if the sample buffer is full.
+  bool offset_ready() const {
+    return start_pos_samples_.size() == max_sample_count_;
+  }
+
  private:
   // This function calculates the start position given the internal state and
   // the provided `latched_encoder' value.