Create app-nolayers documentation

docs/en/Startup-Templates/Application-Single-Layer.md

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+# Application (Single Layer) Startup Template
+
+## Introduction
+
+This template provides a single-layered application for quick start with ABP Framework. 
+
+This document explains the **solution structure** and project in details. If you want to start quickly, you can follow the guides below:
+
+<!-- TODO: Add quick start tutorial link!!! (https://github.com/abpframework/abp/issues/12273) -->
+
+### What is the Difference Between the Application Startup Template?
+
+ABP's [Application Startup Template](Application.md) provides a well-organized and layered solution to create maintainable business applications based on the [Domain Driven Design](../Domain-Driven-Design.md) (DDD) practises. However, some developers find this template little bit complex (or unneccessary) for simple and short-time applications.
+
+In that point, for such applications a single-layered application template is created. Time template has the same functionality, features and modules on runtime with the [Application Startup Template](Application.md) but the development model is minimal and everything is in the single project (`.csproj`).
+
+## How to Start with?
+
+You can use the [ABP CLI](../CLI.md) to create a new project using this startup template. Alternatively, you can directly create & download from the [Get Started](https://abp.io/get-started) page. How to download via CLI is explained in this section.
+
+First, install the ABP CLI if you haven't installed before:
+
+```bash
+dotnet tool install -g Volo.Abp.Cli
+```
+
+Then, use the `abp new` command in an empty folder to create a new solution:
+
+```bash
+abp new Acme.BookStore -t app-nolayers
+```
+
+* `Acme.BookStore` is the solution name, like *YourCompany.YourProduct*. You can use single level, two-levels or three-levels naming.
+* This example specifies the template name (`-t` or `--template` option).
+
+### Specify the UI Framework
+
+This template provides multiple UI frameworks:
+
+* `mvc`: ASP.NET Core MVC UI with Razor Pages
+* `blazor-server`: Blazor Server UI
+* `angular`: Angular UI
+* `none`: Without UI <!-- TODO: try this!!! -!>
+
+> Currently, this template doesn't have Blazor WASM UI, because it requries 3 projects at least (server-side, UI and shared library between these two projects). We'll consider to add Blazor WASM UI support based on your feedback.
+
+Use the `-u` or `ui` option to specify the UI framework, while creating the solution:
+
+```bash
+abp new Acme.BookStore -u angular
+```
+
+* This example specifies the UI type (`-u` option) as `angular`, you can also specify the `mvc` or `blazor-server` for UI type.
+
+### Specify the Database Provider
+
+This template supports the following database providers:
+
+- `ef`: Entity Framework Core (default)
+- `mongodb`: MongoDB
+
+Use the `-d` (or `--database-provider`) option to specify the database provider while creating the solution:
+
+```bash
+abp new Acme.BookStore -d mongodb
+```
+
+## Solution Structure

docs/en/docs-nav.json

@@ -118,6 +118,10 @@
           "text": "Application",
           "path": "Startup-Templates/Application.md"
         },
+        {
+          "text": "Application (Single Layer)",
+          "path": "Startup-Templates/Application-Single-Layer.md"
+        },
         {
           "text": "Module",
           "path": "Startup-Templates/Module.md"