Add "-input=false" to commands in README.md

[artemious7]

If any terraform CLI command requires input, the pipeline will wait indefinitely. The solution is to add -input=false to every applicable terraform command, like so:

terraform plan -out=tfplan -input=false

See the docs for more info.

I think the Readme file here should reflect that. There was a PR to fix the Readme file: #60. The discussion there suggested a solution to use an environment variable to disable requests for input, but it doesn't solve this problem since it has a different purpose (see here)

Fixes #150

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