Docs: Quickstart test run + --via-ir optimizer example

[aryanrahar]

This PR adds two small, newcomer-friendly docs improvements:

Contributing: a “Quickstart: build & run tests once” snippet so first-time contributors can verify their environment quickly.

Using the compiler: a minimal example showing solc --via-ir used with --optimize and --optimize-runs.

Files changed

docs/contributing.rst — quickstart test run block

docs/using-the-compiler.rst — --via-ir + optimizer example (--optimize-runs=1)

Why
New contributors often look for a single command to build & run tests, and many are unsure how --via-ir interacts with optimizer flags. These short, concrete snippets reduce setup friction and align with current usage.

Verification

Built docs locally with:

./docs/docs.sh
✅ Passed (no warnings/errors).

Scope
Docs-only. No changes to compiler code or behavior.

Notes for reviewers
Happy to adjust placement/wording if you prefer a different section heading or example contract.

[github-actions]

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[clonker]

You added your entire venv to the PR. Please fix :)

[aryanrahar]

You added your entire venv to the PR. Please fix :)

Thanks for the heads-up! I removed the accidental .venv and added it to .gitignore. The PR now only contains the two docs changes. CI should be happier now.

[aryanrahar]

all the check have successfully passed!!!

[clonker]

Now your proposed change is gone from the PR (if it was ever there at least), you added some things to the .gitignore - which is unnecessary -, and the commit with your venv is still in the branch. Depending on the size of your example it might be better to propose it here: #16095
Otherwise, please fix, so I can have a look at it or just post it here in the comments. Thanks!