Change all asset links

Assets are served from the root. Hope nobody is serving this site in a subfolder for some reason! :)

_includes/sections/instant-messenger.html

@@ -7,7 +7,7 @@
 <div class="row mb-2">
   {% include card.html color="success"
   title="Mobile: Signal"
-  image="assets/img/tools/Signal.png"
+  image="/assets/img/tools/Signal.png"
   url="https://signal.org"
   footer="OS: Android, iOS, macOS, Windows, Linux"
   description="Signal is a mobile app developed by Open Whisper Systems. The app provides instant messaging, as well as voice and video calling.
@@ -18,7 +18,7 @@
 
   {% include card.html color="primary"
   title="Riot.im"
-  image="assets/img/tools/riot.png"
+  image="/assets/img/tools/riot.png"
   url="https://riot.im/"
   footer="OS: Android, iOS, macOS, Windows, Linux, Web"
   labels="warning:beta:The software is currently in beta and the mobile client states 'End-to-end encryption is in beta and may not be reliable. You should not yet trust it to secure data.'"
@@ -27,7 +27,7 @@
 
   {% include card.html color="warning"
   title="Desktop: Ricochet"
-  image="assets/img/tools/Ricochet.png"
+  image="/assets/img/tools/Ricochet.png"
   url="https://ricochet.im/"
   footer="OS: Windows, macOS, Linux."
   description='Ricochet uses the <a href="#browser"><i class="fas fa-link"></i> Tor network</a> to reach your contacts without relying on messaging servers. It creates a hidden service, which is used to rendezvous with