Improve variable names and comments in blob code

No functional changes whatsoever.

Change-Id: I71f7d106c2e6eb371a248f7e47ed15f152566f6f
diff --git a/aos/vision/blob/disjoint_set.h b/aos/vision/blob/disjoint_set.h
index ed15caf..38cca1d 100644
--- a/aos/vision/blob/disjoint_set.h
+++ b/aos/vision/blob/disjoint_set.h
@@ -6,7 +6,7 @@
 namespace aos {
 namespace vision {
 
-// Disjoint set algorithm:
+// Disjoint set algorithm, which is similar to what this class does:
 // https://en.wikipedia.org/wiki/Disjoint-set_data_structure
 class DisjointSet {
  public: