docs: added info on 3.0 openapi removal (orval-labs#2756)

* docs: added info on 3.0 openapi removal

* docs: added pr link to migration

* docs: fix null docs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* docs: nullable fix

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: Georgegriff

docs/src/pages/versions/v8.mdx

@@ -307,7 +307,30 @@ If you were using dynamic imports:
 - **Future-proof**: Aligns with JavaScript ecosystem standards
 - **Stricter module boundaries**: Better encapsulation and type safety
 
-### 2. Changed default value of httpClient from `axios` to `fetch`
+### 2. OpenAPI 3.0 Support Dropped in Favor of 3.1.0
+
+Support for OpenAPI 3.0 specifications has been dropped in favor of the newer 3.1.0 standard. See [PR #2614](https://github.com/orval-labs/orval/pull/2614) for details.
+
+#### How to migrate
+
+If you're consuming APIs that use OpenAPI 3.0 specifications, you may need to update them to OpenAPI 3.1.0. 
+
+A common issue is replacing `nullable: true`:
+
+```yaml
+# OpenAPI 3.0
+field:
+  type: string
+  nullable: true
+
+# OpenAPI 3.1.0
+field:
+  type: ["string", "null"]
+```
+
+For a complete migration guide, see the [official OpenAPI migration documentation](https://www.openapis.org/blog/2021/02/16/migrating-from-openapi-3-0-to-3-1-0).
+
+### 3. Changed default value of httpClient from `axios` to `fetch`
 
 We changed the default httpClient from `axios` to `fetch` to reduce bundle size and eliminate the need for additional dependencies.
 
@@ -329,7 +352,7 @@ export default {
 };
 ```
 
-### 3. Removed `override.fetch.explode` option
+### 4. Removed `override.fetch.explode` option
 
 This parameter was kept only for compatibility. Since compatibility maintenance is no longer needed in major versions, it has been removed.
 
@@ -349,7 +372,7 @@ paths:
             type: array
 ```
 
-### 4. Changed default value of `override.mock.delay` from `1000` to `false`
+### 5. Changed default value of `override.mock.delay` from `1000` to `false`
 
 We disabled the default delay as it creates noise.
 
@@ -369,7 +392,7 @@ export default {
 };
 ```
 
-### 5. Removed `override.coerceTypes`
+### 6. Removed `override.coerceTypes`
 
 This was removed as it has been replaced by the more flexible and explicit `override.zod.coerce`.
 
@@ -398,7 +421,7 @@ export default {
 };
 ```
 
-### 6. Removed `override.useNativeEnums`
+### 7. Removed `override.useNativeEnums`
 
 This was removed as it has been integrated into `enumGenerationType`.
 
@@ -419,7 +442,7 @@ export default {
 };
 ```
 
-### 7. Changed combined types generation (anyOf/oneOf/allOf)
+### 8. Changed combined types generation (anyOf/oneOf/allOf)
 
 Combined types (`anyOf`, `oneOf`, `allOf`) are now inlined by default instead of creating intermediate type aliases.
 
@@ -439,7 +462,7 @@ export default {
 };
 ```
 
-### 8. Zod Schema Naming Convention Changed to PascalCase
+### 9. Zod Schema Naming Convention Changed to PascalCase
 
 All Zod schema exports now use PascalCase naming convention to align with TypeScript type definition standards.
 
@@ -456,7 +479,7 @@ All Zod schema exports now use PascalCase naming convention to align with TypeSc
 + export type CreatePetsBody = zod.infer<typeof CreatePetsBody>
 ```
 
-### 9. SWR custom error types are no longer generated by default
+### 10. SWR custom error types are no longer generated by default
 
 Custom error type aliases (e.g., `ListPetsQueryError`, `CreatePetsMutationError`) are no longer generated by default as they simply re-export the error type without providing additional value.