Merge pull request #1727 from pypa/dont-require-platform

Don't require `--platform` when running on a development machine

docs/options.md

@@ -184,7 +184,7 @@ Options: `auto` `linux` `macos` `windows`
 
 Default: `auto`
 
-`auto` will auto-detect platform using environment variables, such as `TRAVIS_OS_NAME`/`APPVEYOR`/`CIRCLECI`.
+`auto` will build wheels for the current platform.
 
 - For `linux`, you need [Docker or Podman](#container-engine) running, on Linux, macOS, or Windows.
 - For `macos` and `windows`, you need to be running on the respective system, with a working compiler toolchain installed - Xcode Command Line tools for macOS, and MSVC for Windows.
@@ -192,7 +192,7 @@ Default: `auto`
 This option can also be set using the [command-line option](#command-line) `--platform`. This option is not available in the `pyproject.toml` config.
 
 !!! tip
-    You can use this option to locally debug your cibuildwheel config, instead of pushing to CI to test every change. For example:
+    You can use this option to locally debug your cibuildwheel config on Linux, instead of pushing to CI to test every change. For example:
 
     ```bash
     export CIBW_BUILD='cp37-*'
@@ -200,6 +200,8 @@ This option can also be set using the [command-line option](#command-line) `--pl
     cibuildwheel --platform linux .
     ```
 
+    Linux builds are the easiest to test locally, because all the build tools are supplied in the container, and they run exactly the same locally as in CI.
+
     This is even more convenient if you store your cibuildwheel config in [`pyproject.toml`](#configuration-file).
 
     You can also run a single identifier with `--only <identifier>`. This will