[Dev doc] Add overview and explain repository structure

docs/_docs/development/overview.md

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-title: Overview
+title: Overview and Structure
 layout: docs
 permalink: /development/overview.html
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-<p>👷👷‍♀️Under construction…</p>
+# Framework dependencies:
+
+At its [core](https://github.com/TextureGroup/Texture/blob/master/Texture.podspec#L18), Texture doesn't depend on any non-system frameworks or libraries. Functionalities such as image downloading and caching, video, map and photo assets supports are considered add-ons and extensible by end-users. [By default](https://github.com/TextureGroup/Texture/blob/master/Texture.podspec#L90) Texture includes first-class support for image downloading and caching by integrating [PINRemoteImage](https://github.com/TextureGroup/Texture/blob/master/Texture.podspec#L41) as well as default implementations for other functionalities mentioned above.
+
+# Repository structure
+
+Here are the main directories within the repository:
+- [Source](https://github.com/TextureGroup/Texture/tree/master/Source): All source code of the framework resides here
+  - [Base](https://github.com/TextureGroup/Texture/tree/master/Source/Base): Helper and utility files used throughout the framework.
+  - [Debug](https://github.com/TextureGroup/Texture/tree/master/Source/Debug): Files used for debugging functionalities.
+  - [Details](https://github.com/TextureGroup/Texture/tree/master/Source/Details): Implementaion details of the framework that are exposed to end users.
+  - [Layout](https://github.com/TextureGroup/Texture/tree/master/Source/Layout): Files related to the layout system, including layout-premitives types, layout specs and utility files for Yoga and IGListKit support.
+  - [Private](https://github.com/TextureGroup/Texture/tree/master/Source/Private): Framework-private files that are not exposed to end users, including implementation details, private data structures and helpers.
+  - [TextKit](https://github.com/TextureGroup/Texture/tree/master/Source/TextKit): All files related to TextKit that are used by ASTextNode.
+  - [tvOS](https://github.com/TextureGroup/Texture/tree/master/Source/tvOS): tvOS support.
+  - All other files in the [Source](https://github.com/TextureGroup/Texture/tree/master/Source) directory: Main files that are exposed to end users, including include important components such as nodes (e.g ASDisplayNode, ASButtonNode, ASImageNode, ASCollectionNode and ASTableNode), ASNavigationController, etc.
+- [Tests](https://github.com/TextureGroup/Texture/tree/master/Tests): The framework's test suite, including unit, integration and snapshot test cases.
+- [docs](https://github.com/TextureGroup/Texture/tree/master/docs): Texture documentation that powers [texturegroup.org](https://texturegroup.org/).
+- [examples](https://github.com/TextureGroup/Texture/tree/master/examples): Sample projects on demonstrate how to use various features of the framework.
+- [examples-extra](https://github.com/TextureGroup/Texture/tree/master/examples_extra): More sample projects.
+- All other files in the root directory: Build, CI, git, CocoaPods and Carthage configuration files.
+
+To learn more about main classes and components within the framework, please read other documents under "Development" category.