README: Add BRJ organisation logo.

Author: janbarasek

README.md

@@ -1,3 +1,13 @@
+<div align='center'>
+  <picture>
+    <source media='(prefers-color-scheme: dark)' srcset='https://cdn.brj.app/images/brj-logo/logo-regular.png'>
+    <img src='https://cdn.brj.app/images/brj-logo/logo-dark.png' alt='BRJ logo'>
+  </picture>
+  <br>
+  <a href="https://brj.app">BRJ organisation</a>
+</div>
+<hr>
+
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