Document v3 binary size checks

docs/v3/binary-size.md

@@ -0,0 +1,53 @@
+# Binary Size
+
+Go removes unreachable code during compilation, so the first step is to
+measure the binary you ship instead of assuming a specific feature is expensive.
+
+```sh
+go build -trimpath -o myapp ./cmd/myapp
+ls -lh myapp
+```
+
+For a release-style build, combine reproducible paths with stripped symbol and
+debug information:
+
+```sh
+go build -trimpath -ldflags="-s -w" -o myapp ./cmd/myapp
+ls -lh myapp
+```
+
+Use the Go toolchain to inspect what is in the binary:
+
+```sh
+go version -m myapp
+go tool nm -size myapp | sort -nr | head -40
+```
+
+## Practical Checks
+
+- Run `make check-binary-size` in this repository to compare the current package
+  contribution against the tracked binary-size budget.
+- Build with `-trimpath` for reproducible paths.
+- Use `-ldflags="-s -w"` for release builds when debug symbols are not needed.
+- Keep optional integrations in separate packages when they bring large
+  dependencies.
+- Avoid adding reflection-heavy dependencies to the main command package unless
+  they are required at runtime.
+- Compare sizes from clean builds after each change.
+
+If a specific `urfave/cli` feature appears to keep unexpected code reachable,
+[open an issue](https://github.com/urfave/cli/issues/new) with the Go version,
+build command, a minimal reproduction, and the `go tool nm -size` output that
+shows the largest symbols.
+
+## Current v3 Build Tags
+
+The v3 module does not currently define build tags such as
+`urfave_cli_no_docs`, `urfave_cli_no_completion`, or `urfave_cli_minimal`.
+Documentation generation lives outside the core module in
+[`urfave/cli-docs`](https://github.com/urfave/cli-docs), so applications that
+only import `github.com/urfave/cli/v3` do not pull in that package.
+
+Shell completion support is part of the core package. Leave
+`EnableShellCompletion` disabled unless the application needs shell completion,
+then measure the result with the commands above.

mkdocs.yml

@@ -20,6 +20,7 @@ nav:
   - v3 Manual:
       - Getting Started: v3/getting-started.md
       - Migrating From Older Releases: v3/migrating-from-older-releases.md
+      - Binary Size: v3/binary-size.md
       - Examples:
           - Greet: v3/examples/greet.md
           - Flags: