Update formatting and PDF link in content files

Replaced <br> with <hr> for better separation in 'Writing System.md' and updated the PDF iframe source to an external GitHub link in 'A(A)AMLP Book.md'.

Author: bakisama

content/japanese/Writing System.md

@@ -13,13 +13,14 @@ site: https://learnjapanese.moe/guide/#22-hiragana-and-katakana
 ## Big picture
 Japanese uses **three scripts**:
 - **Hiragana**
-<br>
+<hr>
 <img src="https://learnjapanese.moe/img/hiragana.png">
 - **Katakana**
-<br>
+<hr>
 <img src = "https://learnjapanese.moe/img/katakana.png">
 - **Kanji**
-<br>
+<hr>
+<hr>
 <img src="https://learnjapanese.moe/img/kanji2.jpg">
 <center><i>The first 80 kanji taught to Japanese 1st graders.</i></center>
 

content/learning/ml/A(A)AMLP Book.md

@@ -1,5 +1,5 @@
 <iframe 
-  src="/learning/ml/A(A)AMLP/A(A)AMLP.pdf"
+src="https://raw.githubusercontent.com/abhishekkrthakur/approachingalmost/master/AAAMLP.pdf"
   width="100%"
   height="800px">
 </iframe>