misleading comment corrected (strides in buffer_info is bytes and not number of entries) (#1958)

Author: rikigigi

include/pybind11/buffer_info.h

@@ -21,7 +21,7 @@ struct buffer_info {
     std::string format;           // For homogeneous buffers, this should be set to format_descriptor<T>::format()
     ssize_t ndim = 0;             // Number of dimensions
     std::vector<ssize_t> shape;   // Shape of the tensor (1 entry per dimension)
-    std::vector<ssize_t> strides; // Number of entries between adjacent entries (for each per dimension)
+    std::vector<ssize_t> strides; // Number of bytes between adjacent entries (for each per dimension)
 
     buffer_info() { }