feat: Document publish/subscribe semantics

Author: timonback

src/app/channels/channels.component.css

@@ -4,6 +4,7 @@
     padding: 8px;
     font-size: small;
     font-weight: bold;
+    display: inline-block;
 }
 
 .subscribe-badge {

src/app/channels/channels.component.html

@@ -1,4 +1,23 @@
 <h1>Channels</h1>
+
+<a href="https://www.asyncapi.com/blog/publish-subscribe-semantics" target="_blank">Semantics of publish and subscribe:</a>
+<ul>
+  <li>
+    <span class="badge publish-badge">
+      publish
+      <i class="fa fa-arrow-circle-down"></i>
+    </span>
+    means publish an event to the channel and this application will receive it
+  </li>
+  <li>
+    <span class="badge subscribe-badge">
+     subscribe
+      <i class="fa fa-arrow-circle-up"></i>
+    </span>
+    means subscribe to this channel to receive events published by this application
+  </li>
+</ul>
+
 <mat-accordion>
     <mat-expansion-panel *ngFor="let channel of channels" [id]="channel.anchorIdentifier" [expanded]="selectedChannel == channel.anchorIdentifier" (opened)="this.setChannelSelection(channel)">
         <mat-expansion-panel-header>