Add another comment about substituting Fragment's for MathCommands

...in the LaTeX parser.

Continuation of 838b8da4b16ea69ff754dff7b8a012c4b985e225.
diff --git a/src/services/latex.js b/src/services/latex.js
index 558e86e..75369e8 100644
--- a/src/services/latex.js
+++ b/src/services/latex.js
@@ -1,6 +1,6 @@
 // Parser MathBlock
 var latexMathParser = (function() {
-  function commandToBlock(cmd) {
+  function commandToBlock(cmd) { // can also take in a Fragment
     var block = MathBlock();
     cmd.adopt(block, 0, 0);
     return block;