fixed readme and makefile

[AkashS20]

Notes for Reviewers

This PR fixes #103

• Updated the "Layer Community Welcome Guide" link to Newcomers' Guide in Readme.md
• Updated the play website preview image in Readme.md
• Changed cd.. to cd .. in makefile

Signed commits

• [x] Yes, I signed my commits.

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[leecalcote]

Thanks!