Hi @saikat123x. I see you have removed the library code completely (I guess only temporarily while you work on the problem reported by @sonofcy), but I'll provide some explanation of what was wrong with the structure of the library files prior to their removal.
We can see the library as it was when @sonofcy attempted to install it here:
There are two problems:
Location of Library
The library is in the SDVirtualRAM subfolder of the repository:
It should be in the root of the repository, here:
So everything needs to be moved up one folder level.
This is useful for manual installation as it allows the library to be installed via git clone as you specify. Better yet, it allows installation in an even more convenient manner by downloading the ZIP file produced by GitHub and then using Arduino IDE's "Add .ZIP Library..." feature, as @sonofcy attempted to do.
And if you decide you want to distribute the library via the Arduino Library Manager system, having the library in the root of the repository will be mandatory.
Missing Metadata
Because you placed the code files in the src subfolder, you library has what we call the "recursive layout". It is mandatory for libraries with this layout to have a library.properties metadata file in the root of the library.
You can learn about the library.properties metadata file from the Arduino Library Specification:
https://arduino.github.io/arduino-cli/latest/library-specification/#library-metadata
The correct structure:
SDVirtualRAM/
├── LICENSE
├── README.md
├── examples/
│ └── SDManager_UNO/
│ └── SDManager_UNO.ino
├── library.properties
└── src/
├── SDVirtualRAM.cpp
└── SDVirtualRAM.h