Fix documentation for python platform (#3220)
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## Summary
The option `--platform` for `uv pip compile` was added in #3111 and was
later renamed to `--python-platform` #3146.
This PR updates the documentation such that the listed option is working
again.
## Test Plan
```bash
❯ uv --version
uv 0.1.37 (645d0399f 2024-04-23)
```
Before:
```bash
❯ uv pip compile requirements.in --platform=linux
error: unexpected argument '--platform' found
tip: to pass '--platform' as a value, use '-- --platform'
Usage: uv pip compile <SRC_FILE>...
For more information, try '--help'.
```
After:
```bash
❯ uv pip compile requirements.in --python-platform=linux
Resolved 1 package in 215ms
# This file was autogenerated by uv via the following command:
# uv pip compile requirements.in --python-platform=linux
uv==0.1.37
```
