Add information about alt text to alt text modal in web UI (#33702)

app/javascript/mastodon/locales/en.json

@@ -414,6 +414,8 @@
   "ignore_notifications_modal.not_followers_title": "Ignore notifications from people not following you?",
   "ignore_notifications_modal.not_following_title": "Ignore notifications from people you don't follow?",
   "ignore_notifications_modal.private_mentions_title": "Ignore notifications from unsolicited Private Mentions?",
+  "info_button.label": "Help",
+  "info_button.what_is_alt_text": "<h1>What is alt text?</h1> <p>Alt text provides image descriptions for people with vision impairments, low-bandwidth connections, or those seeking extra context.</p> <p>You can improve accessibility and understanding for everyone by writing clear, concise, and objective alt text.</p> <ul> <li>Capture important elements</li> <li>Summarize text in images</li> <li>Use regular sentence structure</li> <li>Avoid redundant information</li> <li>Focus on trends and key findings in complex visuals (like diagrams or maps)</li> </ul>",
   "interaction_modal.action.favourite": "To continue, you need to favorite from your account.",
   "interaction_modal.action.follow": "To continue, you need to follow from your account.",
   "interaction_modal.action.reblog": "To continue, you need to reblog from your account.",