[Enhancement] Provide examples of how to use TransformerX

[soran-ghaderi]

Is your feature request related to a problem? Please describe.
There are no examples of how to use the library

Describe the solution you'd like
Provide simple examples of how to create encoder/decoder models using TransformerX

• Encoder-only Classifier #113
• Basic Encoder-Decoder Model
• Customized Transformer Architecture
• Training a Transformer Model
• Transfer Learning with TransformerX
• Finetuning using TransformerX
• Integration of TransformerX with Transformers, Tensorflow, Pytorch, etc.

Additional context
Enrich the readme.md file with new ready-to-run and simple examples