Docs : update the steps in Dev.md as per .env.example

[ArslanYM]

Overview
After #2429 , the env examples have been set for local development. But the Dev.md has not been updated as per the new changes.

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For example,

This command doesnt work because an .env.sample doesnt exist.
Rather, the developer has to just copy the content of .env.example already provided. Therefore the docs can be misleading.

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Additional info

Also if allowed I can create a video providing steps to get each keys from respective websites to get started with local dev.

[ArslanYM]

Will be closed after #2440