Extend FAQ by performance calculation method

apps/client/src/app/pages/faq/overview/faq-overview-page.html

@@ -40,6 +40,21 @@
           <a [routerLink]="routerLinkFeatures">here</a>.
         </mat-card-content>
       </mat-card>
+      <mat-card appearance="outlined" class="mb-3">
+        <mat-card-header>
+          <mat-card-title
+            >Which calculation method does Ghostfolio use for
+            performance?</mat-card-title
+          >
+        </mat-card-header>
+        <mat-card-content
+          >Ghostfolio uses the <i>Return on Average Investment</i> (ROAI)
+          calculation method based on the average amount of capital invested
+          over time. ROAI aims to provide a more insightful view of investment
+          performance than simpler approaches, especially when contributions are
+          made over time.</mat-card-content
+        >
+      </mat-card>
       <mat-card appearance="outlined" class="mb-3">
         <mat-card-header>
           <mat-card-title>Can I use Ghostfolio anonymously?</mat-card-title>