feat(diagnostics): Add guide for the diagnostics card (#214)

guides/_subsections/perform-garbage-collection.md

@@ -0,0 +1,33 @@
+## [Perform Garbage Collection](#perform-garbage-collection)
+<ol>
+    <li>
+      {% capture perform-garbage-collection-text %}
+      <p>
+        The <i>Diagnostics</i> <code>card</code> allows 
+        you to perform diagnostic operations on a <code>target</code> <b>JVM</b> through remote access to supported <b>Java MXBeans</b>.
+      </p>
+      <p>
+        Currently <b>Cryostat</b> supports invoking garbage collection on <code>target</code> <b>JVMs</b>.
+      </p>
+      {% endcapture %}
+      {% include howto_step.html
+        summary="Add the <i>Diagnostics</i> <code>Card</code>"
+        image-name="4.0.0/dashboard/add-diagnostics-card.png"
+        caption="Click on the <i>Diagnostics</i> <code>card</code> for a preview."
+        text=perform-garbage-collection-text
+      %}
+    </li>
+    <li>
+      {% capture diagnostics-card-finish %}
+      <p>
+        After clicking <i>Finish</i>, the <code>card</code> will be added to the dashboard. You can click the <i>Start Garbage Collection</i> button in the middle of the <code>card</code> at any time to trigger a garbage collection cycle.
+    </p>
+    {% endcapture %}
+    {% include howto_step.html
+      summary="Finish <code>Card</code> Creation"
+      image-name="4.0.0/dashboard/diagnostics-card.png"
+      caption="The <i>Diagnostics</i> <code>card</code> displayed on the dashboard."
+      text=diagnostics-card-finish
+    %}
+    </li>
+</ol>

guides/index.md

@@ -59,5 +59,7 @@ common actions and workflows of interest and why they are useful.
 
 {% include_relative _subsections/using-smart-triggers.md %}
 
+{% include_relative _subsections/perform-garbage-collection.md %}
+
 [comment]: # ## [Analyze Recordings Online](#analyze-recordings-online)
 [comment]: # TODO