chore: update docs (#111)

## Description

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relates to #1234

## Checklist

- [ ] Issue was linked above
- [ ] Code format was applied: `make fmt`
- [ ] Examples were added / adjusted (see `examples/` directory)
- [x] Docs are up-to-date: `make generate-docs` (will be checked by CI)
- [ ] Unit tests got implemented or updated
- [ ] Acceptance tests got implemented or updated (see e.g. [here](f5f99d1709/stackit/internal/services/dns/dns_acc_test.go))
- [x] Unit tests are passing: `make test` (will be checked by CI)
- [x] No linter issues: `make lint` (will be checked by CI)

Co-authored-by: Marcel S. Henselin <marcel.henselin@stackit.cloud>
Reviewed-on: #111

examples/resources/stackitprivatepreview_sqlserverflexbeta_instance/resource.tf

@@ -1,3 +1,28 @@
+# NOTE: flavor handling will change in future
+# V2 compatible flavor usage
+resource "stackitprivatepreview_sqlserverflexbeta_instance" "instance" {
+  project_id      = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
+  name            = "example-instance"
+  backup_schedule = "0 3 * * *"
+  retention_days  = 31
+  flavor = {
+    cpu = 2
+    ram = 4
+  }
+  storage = {
+    class = "premium-perf2-stackit"
+    size  = 50
+  }
+  version = 2022
+  network = {
+    acl          = ["XXX.XXX.XXX.X/XX", "XX.XXX.XX.X/XX"]
+    access_scope = "SNA"
+  }
+}
+
+# future use of flavor (implemented in V3 API)
+# first determine flavor and then use the flavor_id
+
 # without encryption and SNA
 resource "stackitprivatepreview_sqlserverflexbeta_instance" "instance" {
   project_id      = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"