Lack of Local Build Instructions in README.md

While README.md links to a "Getting Started" guide, it does not contain direct build commands or installation instructions inline.

Add a short "Quick Start" build section with:
(Bash/terminal)
git clone https://github.com/facebook/infer.git
cd infer
./build-infer.sh

Improves DX (developer experience) and encourages first-time contributors to try building it quickly.