Add TODO checkboxes to Python/C++ sub-headings

- roadmap.org: *** TODO Python and *** TODO C++ with [/] cookie
  on each problem heading for [0/2] progress tracking
- Note files now have TODO Approach, TODO Python, TODO C++
  sections for structured problem solving

org/cpp/dsa/sliding-window/0003-longest-substring-without-repeating-characters.org

@@ -3,6 +3,15 @@
 :NEETCODE: [[../../../../leetcode/out/roadmap.org::*0003. Longest Substring Without Repeating Characters][Roadmap]]
 :END:
 
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
 #+begin_src cpp
 
 #+end_src

org/cpp/dsa/sliding-window/0076-minimum-window-substring.org

@@ -3,6 +3,15 @@
 :NEETCODE: [[../../../../leetcode/out/roadmap.org::*0076. Minimum Window Substring][Roadmap]]
 :END:
 
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
 #+begin_src cpp
 
 #+end_src

org/cpp/dsa/sliding-window/0121-best-time-to-buy-and-sell-stock.org

@@ -3,6 +3,15 @@
 :NEETCODE: [[../../../../leetcode/out/roadmap.org::*0121. Best Time to Buy And Sell Stock][Roadmap]]
 :END:
 
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
 #+begin_src cpp
 
 #+end_src

org/cpp/dsa/sliding-window/0239-sliding-window-maximum.org

@@ -3,6 +3,15 @@
 :NEETCODE: [[../../../../leetcode/out/roadmap.org::*0239. Sliding Window Maximum][Roadmap]]
 :END:
 
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
 #+begin_src cpp
 
 #+end_src

org/cpp/dsa/sliding-window/0424-longest-repeating-character-replacement.org

@@ -3,6 +3,15 @@
 :NEETCODE: [[../../../../leetcode/out/roadmap.org::*0424. Longest Repeating Character Replacement][Roadmap]]
 :END:
 
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
 #+begin_src cpp
 
 #+end_src

org/cpp/dsa/sliding-window/0567-permutation-in-string.org

@@ -3,6 +3,15 @@
 :NEETCODE: [[../../../../leetcode/out/roadmap.org::*0567. Permutation In String][Roadmap]]
 :END:
 
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
 #+begin_src cpp
 
 #+end_src

org/cpp/dsa/sliding-window/3306-count-of-substrings-containing-every-vowel-and-k-consonants-ii.org

@@ -3,6 +3,15 @@
 :NEETCODE: [[../../../../leetcode/out/roadmap.org::*3306. Count of Substrings Containing Every Vowel and K Consonants II][Roadmap]]
 :END:
 
+** TODO Approach
+Write your approach here.
+
+** TODO Python
+#+begin_src python
+
+#+end_src
+
+** TODO C++
 #+begin_src cpp
 
 #+end_src