adds comment

documentation/sphinx_static/convergence_particles.rst

@@ -123,8 +123,12 @@ class cannot search for the source parameters itself.
 Thirdly, I will note that one may in fact break this call by modifying
 the `iter0` and `checkpoints_per_file` values, since we have explicitly
 placed `iter0` in the `checkpoint` 0 file.
-However, a full discussion of the `iter0` and `checkpoint` subtleties is
-beyond the scope of this tutorial.
+While a full discussion of the `iter0` and `checkpoint` subtleties is
+beyond the scope of this tutorial, I will mention that it was a
+conscious choice to use a simple `iteration` to `checkpoint`
+correspondence, since we don't actually need anything smarter outside of
+extreme scenarios that need to be addressed individually anyway
+due to other complexities.
 
 .. code:: python