docs: improve environment setup and add .env.example files

[shubham5080]

Is there an existing issue for this?

• I have searched the existing issues

Issue Description ✍️

Added .env.example to blockchain and client

Made environment setup clearer

Explained dummy vs real keys

Updated README accordingly

Improved new contributor onboarding

Record

• I have synced all my node versions as mentioned in the project
• I am using the same version of npm as is the project
• My current branch is in sync with the development branch
• I want to work on this issue

[shubham5080]

“Can I get this issue assigned to me?”

[shubham5080]

i THINK this env.example having in project and instruction according to the it in readme help the new contributer from waste unwanted time ,

[shubham5080]

ok sir i read the README.md carefully and i saw that if there is documentation issue or small updated then SUBMIT the PR so now i am doing it .