SUMMARY: Add pahole to the list

It was already in `Contributing.md`, so add it here too. Rename the
section so that it makes a bit more sense.

Signed-off-by: Miguel Ojeda <[email protected]>

Author: ojeda

SUMMARY.md

@@ -89,11 +89,12 @@
   - [Rust index](https://lwn.net/Kernel/Index/#Development_tools-Rust)
   - [Kangrejos index](https://lwn.net/Archives/ConferenceIndex/#Kangrejos)
 
-## Toolchains
+## Tools and toolchains
 
   - [kernel.org prebuilt LLVM+Rust](https://kernel.org/pub/tools/llvm/rust/)
   - [`rustc_codegen_gcc`](https://github.com/rust-lang/rustc_codegen_gcc)
   - [Rust GCC](https://rust-gcc.github.io)
+  - [`pahole`](https://github.com/acmel/dwarves)
 
 ## Other trees