add Facebook link

src/Introduction.sass

@@ -0,0 +1,42 @@
+.Introduction__chart
+  max-width: 1429px
+  width: 80%
+
+.Introduction__footer
+  margin: 1em 10%
+  text-align: center
+
+.BAdWIcon__image
+  width: 350px
+
+.LMUIcon__image
+  text-align: right
+  width: 200px
+
+.HumboldtIcon__image
+  width: 200px
+  padding-bottom: 1em
+
+.HumboldtIcon::after
+  content: '\a'
+  white-space: pre
+
+.Auth0Badge,
+.Auth0Badge__image
+  height: 50px
+  width: 150px
+
+.icon
+  &__large
+    font-size: 2.5em
+    margin-right: .2rem
+  &__twitter
+    vertical-align: middle
+    color: #212529
+
+    &:hover
+      color: #212529
+
+.eblInfo
+  vertical-align: middle
+  padding-right: 1em

src/Introduction.tsx

@@ -6,7 +6,7 @@ import BAdWLogoBlue from 'BAdW_Logo_blue.svg'
 import AvHLogo from 'AvH_Logo.svg'
 import LRZLogoBlue from 'lrz_wortbild_d_blau-230.png'
 
-import './Introduction.css'
+import './Introduction.sass'
 import { Col, Row } from 'react-bootstrap'
 import { HeadTags } from 'router/head'
 
@@ -77,12 +77,24 @@ function Auth0Badge(): JSX.Element {
 function TwitterIcon(): JSX.Element {
   return (
     <ExternalLink
-      className="TwitterIcon"
+      className="icon__twitter"
       href="https://twitter.com/ebl_info?ref_src=twsrc%5Etfw"
       title="eBL Twitter account"
     >
-      <i className="fab fa-x-twitter" />
-      <span className="eblInfo"> @eBL_info</span>
+      <i className="fab fa-x-twitter icon__large" />
+      <span className="eblInfo">@eBL_info</span>
+    </ExternalLink>
+  )
+}
+
+function FacebookIcon(): JSX.Element {
+  return (
+    <ExternalLink
+      href="https://www.facebook.com/profile.php?id=61556323986355"
+      title="eBL Facebook account"
+    >
+      <i className="fab fa-facebook icon__large" />
+      <span className="eblInfo">CAIC on Facebook</span>
     </ExternalLink>
   )
 }
@@ -170,6 +182,11 @@ export default function Introduction(): JSX.Element {
             <Auth0Badge />
           </Col>
         </Row>
+        <Row>
+          <Col>
+            <FacebookIcon />
+          </Col>
+        </Row>
       </footer>
     </AppContent>
   )