Added gulp build to README

[RajatArora08]

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Please describe your changes here:
Adds gulp build to README #117

[aslafy-z]

Thank you for your PR. Sadly, I think these changes aren't needed. Would you please explain your motivation for editing these ? Have you tried to run the project ?

[aslafy-z]

This does not build the webserver but the website.

[aslafy-z]

This build command is not needed. Calling only gulp will build the assets and serve it through a webserver. Calling gulp build will only build the assets, it does a production build.

[aslafy-z]

Also, I did some enhancements to this doc in #76 . Feel free to check and comment .

[RajatArora08]

@aslafy-z Thanks for the review! I guess the Docker is not yet merged on the repo hence I didn't see it.
Regarding this issue, I did a clean install of the repo, but gulp fails with the issue Error: File not found with singular glob: ~/swag-for-dev/site/dist . After your comment, I digged down into the issue and I believe the issue is because gulp default task runs in parallel and the webserver starts before the files are built into the dist directory. I created another PR (#121) for the fix that worked for me.