cautionary notice about new Fly pricing

docs/install/fly.md

@@ -8,7 +8,18 @@
 
 ### Creating a Fly.io Account
 
-First, you’ll need to sign up for an account. Go to [fly.io](https://fly.io) and click “Get Started,” then fill in the form. Note that Fly may require you to enter credit card details. See [their docs on how they use credit cards](https://fly.io/docs/about/credit-cards/) for more information. If you follow the steps in this guide, you will remain well within the free plan limits. For more details, check out [Fly’s pricing documentation](https://fly.io/docs/about/pricing/).
+:::caution
+At the time of writing (2024-02-06), Fly's new pricing structure is not clearly communicated.
+They've updated their docs, which state that [new customers are *credited* $5, so they can try Fly at *no cost*](https://fly.io/docs/about/pricing/#new-customers).
+However, as [clarified by Fly staff](https://community.fly.io/t/i-got-charged-today-for-the-hobby-plan-and-im-confused-as-to-why-cause-fly-io-didnt-send-any-emails/17969/8?u=tjex) on the Fly forum, new accounts are indeed charged $5 per month + any usage that exceeds the free allowances.
+
+This means it is no longer possible to use Fly for free within the "free allowance" limits. There is now a base $5 fee per month. Any usage outside the "free allowance" is billed accordingly ontop of the monthly $5 fee.
+
+See [Fly's pricing page](https://fly.io/docs/about/pricing/#new-customers) for further details.
+:::
+
+To begin, you’ll need to sign up for an account. Go to [fly.io](https://fly.io) and click “Get Started,” then fill in
+the form. Note that Fly requires that credit card details for sign up. See [their docs on how they use credit cards](https://fly.io/docs/about/credit-cards/) for more information.
 
 ### Accessing the `fly` command line tool