Typo, brief description of implementations.

source/Dive_into_Functions.rst

@@ -497,7 +497,7 @@ Write a program that calculates the similarity of 2 RNA sequences.
   so you have to compare the first base of two sequences and use the matrix to get the similarity
   from the similarity table, on so on for all bases then sum these similarities.
 
-First implementation
+First implementation (list of columns)
 
 .. literalinclude:: _static/code/matrix.py
    :linenos:
@@ -506,7 +506,7 @@ First implementation
 :download:`matrix.py <_static/code/matrix.py>` .
 
 
-Second implementation
+Second implementation (bad variable naming, no documentation)
 
 .. literalinclude:: _static/code/matrix2.py
    :linenos:
@@ -515,7 +515,7 @@ Second implementation
 :download:`matrix2.py <_static/code/matrix2.py>` .
 
 
-Thirs implementation
+Third implementation (dict {(row, col): value})
 
 .. literalinclude:: _static/code/matrix3.py
    :linenos: