Update favicon to custom logo and add logo assets

Replaced the emoji favicon with a custom image (cd/logo_icon.png) in _config.yml. Added new logo assets in PDF, PNG, and SVG formats to assets/img/cd/.

Author: shalailahaas

_config.yml

@@ -12,7 +12,7 @@ description: > # the ">" symbol means to ignore newlines until "footer_text:"
 footer_text: 
 keywords: psychiatry, research, mental health # add your own keywords or leave empty
 lang: en # the language of your site (for example: en, fr, cn, ru, etc.)
-icon: 🧠 # the emoji used as the favicon (alternatively, provide image name in /assets/img/)
+icon: cd/logo_icon.png  # the emoji used as the favicon (alternatively, provide image name in /assets/img/)
 
 url: https://mindlabresearch.github.io # the base hostname & protocol for your site
 baseurl:  # the subpath of your site, e.g. /blog/. Leave blank for root