Add documentation about target.$triple.runner

Author: RReverser

src/doc/config.md

@@ -57,15 +57,20 @@ email = "..."
 vcs = "none"
 
 # For the following sections, $triple refers to any valid target triple, not the
-# literal string "$triple", and it will apply whenever that target triple is
+# literal string "$triple", and it will apply whenever that target triple is
 # being compiled to. 'cfg(...)' refers to the Rust-like `#[cfg]` syntax for
 # conditional compilation.
-[target.$triple]
-# This is the linker which is passed to rustc (via `-C linker=`) when the `$triple`
+[target.$triple]
+# This is the linker which is passed to rustc (via `-C linker=`) when the `$triple`
 # is being compiled for. By default this flag is not passed to the compiler.
-linker = ".."
-# Same but for the library archiver which is passed to rustc via `-C ar=`.
+linker = ".."
+# Same but for the library archiver which is passed to rustc via `-C ar=`.
 ar = ".."
+# If a runner is provided, compiled targets for the `$triple` will be executed
+# by invoking the specified runner executable with actual target as first argument.
+# This applies to `cargo run`, `cargo test` and `cargo bench` commands.
+# By default compiled targets are executed directly.
+runner = ".."
 # custom flags to pass to all compiler invocations that target $triple
 # this value overrides build.rustflags when both are present
 rustflags = ["..", ".."]