doc: Be more explicit with available wasm-opt flags

docs/src/cargo-toml-configuration.md

@@ -18,6 +18,10 @@ The available configuration options and their default values are shown below:
 # be set to an array of strings which are explicit arguments to pass to
 # `wasm-opt`. For example `['-Os']` would optimize for size while `['-O4']`
 # would execute very expensive optimizations passes
+#
+# In most cases, the `-O[X]` flag is enough. However, if you require extreme
+# optimizations, see the full list of `wasm-opt` optimization flags
+# https://github.com/WebAssembly/binaryen/blob/version_111/test/lit/help/wasm-opt.test
 wasm-opt = ['-O']
 
 [package.metadata.wasm-pack.profile.dev.wasm-bindgen]