[Glitch] Add more explicit explanations about author attribution and fediverse:creator

Port 8b56509625 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/styles/forms.scss

@@ -23,6 +23,8 @@ code {
   position: relative;
   overflow: hidden;
   height: 160px;
+  max-width: 566px;
+  margin-inline: auto;
 
   &::after {
     content: '';