Move `Docs/ReadMe.txt` to install assets directory

[delphidabbler]

The purpose of ReadMe.txt is to distributed with zip files and be displayed by the installer. Locating the file in the Docs directory does not make its purpose clear. The difference in purpose of README.md and ReadMe.txt is clouded.

Moving ReadMe.txt into the Src/Install/Assets directory would clarify the file's purpose.

[delphidabbler]

Alternatively, there could be a new Installer subdirectory of Docs where ReadMe.txt could be kept, along with License.rtf & UpdatingPreview.rtf that are currently in Src/Install/Assets.

[delphidabbler]

Decided to split ReadMe.txt into two separate documents, one each for the portable and standard editions. The appropriate version will be included in relevant edition's release zip file.

However, it has been decided that moving the read-me files into Install/Assets is not appropriate. While such a move makes sense for the standard edition it does not make sense for the portable edition since no installer is built for that edition.

As a result, this issue is being rejected and closed but new issue #127 has been created with regard to the splitting of ReadMe.txt into two versions.