add DA prefix doc

Author: Shikha Maheshwari

README.md

@@ -21,6 +21,8 @@ You can see the published documentation at https://terraform-ibm-modules.github.
 - Maintaining the GitHub project
     - [Maintainers contribution process](https://terraform-ibm-modules.github.io/documentation/#/maintain-module.md)
     - [About merging pull requests](https://terraform-ibm-modules.github.io/documentation/#/merging.md)
+- Deployable Architecture Reference Docs
+    - [Prefix Usage Guide](https://terraform-ibm-modules.github.io/documentation/#/DA-prefix.md)
 - Reference
     - [Module authoring guidelines](https://terraform-ibm-modules.github.io/documentation/#/implementation-guidelines.md)
     - [Design guidelines](https://terraform-ibm-modules.github.io/documentation/#/design-guidelines.md)

docs/DA-prefix.md

@@ -0,0 +1,38 @@
+# Prefix in Deployable Architecture
+
+The **`prefix`** input variable allows you to prepend a custom string to the names of all resources created by this automation. This is especially useful for:
+
+- **Avoiding naming collisions** when deploying the same solution multiple times within the same account.
+- **Creating identical infrastructure** across multiple regions or environments.
+- **Improving resource traceability** by embedding environment or region identifiers into resource names.
+
+If you do not wish to use a prefix, you may set the value to `null` or an empty string (`""`).
+
+**Important**: The automation automatically inserts a hyphen between the prefix and the resource name. Therefore, you do not need to include a hyphen in the prefix yourself.
+
+### Examples
+
+Here are some common patterns for using the prefix:
+
+- **Environment-based**:
+  - `dev`, `test`, `prod`
+- **Environment + Region**:
+  - `dev-eu-gb`, `prod-us-south`, `test-jp-tok`
+- **Project-specific**:
+  - `webapp-dev`, `ml-prod`, `iot-test`
+- **Team or department identifiers**:
+  - `fin-dev`, `hr-prod`, `eng-test`
+- **Date or version-based** (for temporary or experimental deployments):
+  - `exp-202505`, `v2-dev`
+
+These conventions help ensure that resources are clearly grouped and easily identifiable, especially in shared or multi-tenant accounts.
+
+### Naming Rules
+
+To ensure compatibility and consistency, the prefix must follow these rules:
+
+- Must begin with a **lowercase letter**
+- May contain only **lowercase letters**, **digits**, and **hyphens (`-`)**
+- Must **not end** with a hyphen (`-`)
+- Must **not contain consecutive hyphens** (`--`)
+- Maximum length: **16 characters**