Add data accuracy text to welcome screen

app/src/frontend/pages/welcome.css

@@ -6,12 +6,14 @@
     z-index: 10000;
     top: 0;
     width: 100%;
-    max-height: 100%;
+    max-height: 95%;
+    max-height: calc(100%-2em);
     border-radius: 0;
-    padding: 1.5em 2.5em 2.5em;
     overflow-y: auto;
 }
+
 .welcome-float.jumbotron {
+    padding: 1em 2.5em 1.5em;
     background: #fff;
     background-color: rgba(255,255,255,0.95);
 }
@@ -23,3 +25,7 @@
         top: 1em;
     }
 }
+
+.welcome-float .lead {
+    font-size: 1.15em;
+}

app/src/frontend/pages/welcome.tsx

@@ -22,6 +22,9 @@ const Welcome = () => (
         please read our <a href="https://www.pages.colouring.london/data-ethics">data ethics policy</a> and
         credit Colouring London if you use or share our maps or data.
         </p>
+        <p className="lead">
+            We collect our building data from many sources. Though we are unable to vouch for their accuracy, we are currently experimenting with a range of features including 'data source', 'edit history', and 'entry verification', to assist you in checking reliability and judging how suitable the data are for your intended use.
+        </p>
         <Link to="/view/categories"
             className="btn btn-outline-dark btn-lg btn-block">
             Start Colouring Here!