Update index.md

Adding reference to a repository that is about learning effective java

Signed-off-by: M Saif Asif <[email protected]>

Author: MSaifAsif

collections/dil-dil-pakistan/index.md

@@ -6,6 +6,7 @@ items:
  - alisaifee/flask-limiter
  - ziishaned/learn-regex
  - sarfraznawaz2005/whatspup
+ - MSaifAsif/effective-java-study
 display_name: Dil Dil Pakistan
 created_by: alisaifee
 image: dil-dil-pakistan.png