[docs] add Terraform installation instructions

Summary: We should have Terraform installation instructions in the dev_services.md doc since we use Terraform scripts in our local cloud.

Test Plan: followed these instructions to install Terraform

Reviewers: yayabosh, ashoat

Reviewed By: yayabosh, ashoat

Subscribers: ashoat, palys-swm, Adrian, atul

Differential Revision: https://phab.comm.dev/D4524