feat: add DA prefix doc (#76)

* add DA prefix doc

* added code snippet in prefix doc

* address review comments

* address formatting

---------

Co-authored-by: Shikha Maheshwari <shikhamaheshwari@Shikhas-MacBook-Pro.local>

Author: maheshwarishikha

README.md

@@ -23,6 +23,7 @@ You can see the published documentation at https://terraform-ibm-modules.github.
     - [About merging pull requests](https://terraform-ibm-modules.github.io/documentation/#/merging.md)
 - Reference
     - [Module authoring guidelines](https://terraform-ibm-modules.github.io/documentation/#/implementation-guidelines.md)
+    - [Deployable Architecture authoring guidelines](https://terraform-ibm-modules.github.io/documentation/#/da-implementation-guidelines.md)
     - [Design guidelines](https://terraform-ibm-modules.github.io/documentation/#/design-guidelines.md)
     - [Module structure](https://terraform-ibm-modules.github.io/documentation/#/module-structure.md)
     - [Metadata file (index.yml)](https://terraform-ibm-modules.github.io/documentation/#/module-catalog-metadata.md)

docs/_sidebar.md

@@ -13,6 +13,7 @@
     - [About merging pull requests](merging.md)
 - Reference
     - [Module authoring guidelines](implementation-guidelines.md)
+    - [Deployable Architecture authoring guidelines](da-implementation-guidelines.md)
     - [Design guidelines](design-guidelines.md)
     - [Module structure](module-structure.md)
     - [Metadata file (index.yml)](module-catalog-metadata.md)

docs/da-implementation-guidelines.md

@@ -0,0 +1,71 @@
+# Deployable Architecture authoring guidelines
+
+## 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**
+
+Here is the code snippet for your reference.
+
+```hcl
+variable "prefix" {
+  type        = string
+  nullable    = true
+  description = "The prefix to be added to all resources created by this solution. To skip using a prefix, set this value to null or an empty string. The prefix must begin with a lowercase letter and may contain only lowercase letters, digits, and hyphens '-'. It should not exceed 16 characters, must not end with a hyphen('-'), and can not contain consecutive hyphens ('--'). Example: prod-0205-cos."
+
+  validation {
+  # - null and empty string is allowed
+  # - Must not contain consecutive hyphens (--): length(regexall("--", var.prefix)) == 0
+  # - Starts with a lowercase letter: [a-z]
+  # - Contains only lowercase letters (a–z), digits (0–9), and hyphens (-) 
+  # - Must not end with a hyphen (-): [a-z0-9]
+  condition = (var.prefix == null || var.prefix == "" ? true :
+    alltrue([
+      can(regex("^[a-z][-a-z0-9]*[a-z0-9]$", var.prefix)),
+      length(regexall("--", var.prefix)) == 0
+    ])
+  )
+  error_message = "Prefix must begin with a lowercase letter and may contain only lowercase letters, digits, and hyphens '-'. It must not end with a hyphen('-'), and cannot contain consecutive hyphens ('--')."
+ }
+ 
+  validation {
+   # must not exceed 16 characters in length
+    condition = length(var.prefix) <= 16
+    error_message = "Prefix must not exceed 16 characters."
+  }
+}
+```