[Internal] Add Well Known Types Documentation (#4775)

## Changes
<!-- Summary of your changes that are easy to understand -->
Add a README.md section on well known types

## Tests
<!-- 
How is this tested? Please see the checklist below and also describe any
other relevant tests
-->

- [ ] `make test` run locally
- [ ] relevant change in `docs/` folder
- [ ] covered with integration tests in `internal/acceptance`
- [ ] using Go SDK
- [ ] using TF Plugin Framework
NO_CHANGELOG=true

Author: rauchy

README.md

@@ -99,3 +99,43 @@ If you didn't check-in [`.terraform.lock.hcl`](https://www.terraform.io/language
 ## Use of Terraform exporter
 
 The exporter functionality is experimental and provided as is. It has an evolving interface, which may change or be removed in future versions of the provider.
+
+## Well-Known Types
+
+### Duration Fields
+
+Duration fields accept Go-style duration strings. Use standard time units like `s` (seconds), `m` (minutes), `h` (hours).
+
+```hcl
+resource "databricks_example" "this" {
+  timeout_duration = "30m"      # 30 minutes
+  retry_delay     = "10s"       # 10 seconds  
+  max_lifetime    = "24h"       # 24 hours
+  short_timeout   = "500ms"     # 500 milliseconds
+}
+```
+
+### Timestamp Fields
+
+Timestamp fields require RFC3339 formatted datetime strings. Include timezone information for best results.
+
+```hcl
+resource "databricks_example" "this" {
+  start_time    = "2023-10-15T14:30:00Z"           # UTC timezone
+  end_time      = "2023-10-15T14:30:00-07:00"      # Pacific timezone
+  created_at    = "2023-10-15T14:30:00.123Z"       # With milliseconds
+}
+```
+
+### JSON Value Fields
+
+JSON value fields accept JSON-encoded strings. The provider will normalize and validate the JSON structure.
+
+```hcl
+resource "databricks_example" "this" {
+  settings = jsonencode({
+    enabled = true
+    options = ["option1", "option2"]
+  })
+}
+```