Feature/task 865 simple document (#94)

* restarted to organize documents

* reorganizing folder structure and removed Japanese documents tentattively.

* Updated System-requirements.md

* updated index.md

* updated system-requierments.md

* Added sample-installation.md

* Added installation.md

* fixed filename Intallation.md to Installation.md

* adde whats new.

* deleted some super tips images from the document and image folder.

* edited UT2018_UTS2_SuperTips_13.png and added texts in introduction.md

* made that part to be a table.

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* deleted How to create a texture with alpha channel in introduction.md

* removed 0.2.0 from whats-new.md

* deleted an emacs backup file.

* Added images for the box light document.

* updated the doc.

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* edited whats-new-0.4.0.md

* Updated TableOfContents.md

* updated instruction.md

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* ecited texts over  UT2018_UTS_SuperTips_10.png

* replaced some double quote in introduction.md to **

* deleted an unnecessary emacs backup file.

* updated introduction.md

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* replaced some " to ** in instruction.md

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* Fixed: typo in CHANGELOG.md

* Replacing some images which were with Japanese text

* Update images for stencil technique. UPP_image036

* Based Unity version for DXR is 2020.3.23f1.

* removed a youtube clip thumbnail

* Updated base Unity version 2021.2.3 for some test projects.

* Updated HdrpDX12GraphicsTest-202.2 and made it  compatible with 2021.2.3f1

Author: H3idi-X