docs(ins): add faq for gpu billing

Author: bene2k1

pages/instances/faq.mdx

@@ -50,14 +50,23 @@ Instances are billed on a pay-as-you-go basis, and their prices are made up of t
 
 You can change the storage type and flexible IP after the Instance creation, which may affect the monthly billing.
 
+## How are Instances billed?
+
+Instances are billed according to the time they are powered on:
+
+- **CPU Instances**: Charged per hour while powered on or in standby.
+- **GPU Instances**: Charged per minute while powered on or in standby.
+
+Note, that while compute resources follow this usage-based model, other resources—such as IP addresses and storage—are billed for the entire duration they remain allocated to your account, even if the Instance is powered off.
+For more information about Instance billing, refer to the [Instances pricing page](https://www.scaleway.com/en/pricing/virtual-instances/)
 
 ### What are the prices for Instances?
 
-Refer to the [Pricing page](https://www.scaleway.com/en/pricing/virtual-instances/) to learn about the cost of each Instance type.
+Refer to the [pricing page](https://www.scaleway.com/en/pricing/virtual-instances/) to learn about the cost of each Instance type.
 
 ### What are the storage prices for Instances?
 
-Refer to the [Pricing page](https://www.scaleway.com/en/pricing/storage/) to learn about the storage fees for Instances.
+Refer to the [pricing page](https://www.scaleway.com/en/pricing/storage/) to learn about the storage fees for Instances.
 
 ### How much does a flexible IP cost?