docs: wrap long words instead of overflowing

This fixes rendering on mobile for the 24.1.1 release notes, where we'd
otherwise end up with horizontal scrolling.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29573>

docs/mesa3d_theme/static/rst.css

@@ -54,6 +54,10 @@ main .container {
   padding: 0;
 }
 
+main.body {
+  overflow-wrap: break-word;
+}
+
 li > p:last-of-type,
 th > p:last-of-type,
 td > p:last-of-type,