Quick Start Page Needs Some TLC, IMO

### What do you see as an issue? <img width="1638" height="862" alt="Image" src="https://github.com/user-attachments/assets/12b7fc5b-3fd8-4d17-8116-32febf935206" /> Hey! Airflow user here. The quick start page is the most important documentation page of any project, and Airflow's needs some love. I'm volunteering to fix it, this issue will document some of my changes. A quick start page is reflects the bare minimum required to install the project and get it running. See, for example, [pandas](https://pandas.pydata.org/docs/getting_started/index.html), [numpy](https://numpy.org/install/), or [jupyter](https://jupyter.org/install). There is no discussion of versions or extras or pinned dependencies. That goes somewhere else. Specific Issues: 1. Grammar: "methods is" should be "methods are". 2. the "\` or \`\`uv\`\`" in the source file appears to be missing here, for reasons I don't understand. 3. The install command should be a copyable code block. 4. Beginners do not usually understand `[EXTRAS]`. They don't know that `EXTRAS` needs to be replaced with real values, and this page does not explain that the options are any of `async, graphviz, kerberos, memray, gunicorn, otel, statsd` or `all`. One could define a bash variable earlier in the code block called `EXTRAS` and refer to it here as `$EXTRAS`, but that is seriously overkill for a quick start page. A simple list will do, if you mention it at all. 5. Someone visiting the quick start page wants the most recent airflow version. If they wanted something else, they would be on a different page. Also, it's not clear to some users that AIRFLOW_VERSION needs to be replaced. It isn't wrapped in `<THE_REGULAR_SYNTAX>` for a required replacement or set as a `$VARIABLE`. Like EXTRAS, this is a potential stumbling block. A simple `pip install apache-airflow` will download the most recent version by default. Requiring a pin here for the quick start page increases documentation maintenance surface area and makes life difficult…