Rollup merge of #137991 - tgross35:avr-book-links, r=jieyouxu

Add `avr-none` to SUMMARY.md and platform-support.md

This was missed this in the implementation PR, so update the links here.

Author: workingjubilee

src/doc/rustc/src/SUMMARY.md

@@ -50,6 +50,7 @@
     - [\*-linux-ohos](platform-support/openharmony.md)
     - [\*-hurd-gnu](platform-support/hurd.md)
     - [aarch64-unknown-teeos](platform-support/aarch64-unknown-teeos.md)
+    - [avr-none](platform-support/avr-none.md)
     - [\*-espidf](platform-support/esp-idf.md)
     - [\*-unknown-fuchsia](platform-support/fuchsia.md)
     - [\*-unknown-trusty](platform-support/trusty.md)

src/doc/rustc/src/platform-support.md

@@ -301,7 +301,7 @@ target | std | host | notes
 [`armv8r-none-eabihf`](platform-support/armv8r-none-eabihf.md) | * |  | Bare Armv8-R, hardfloat
 [`armv7a-nuttx-eabi`](platform-support/nuttx.md) | ✓ |  | ARMv7-A with NuttX
 [`armv7a-nuttx-eabihf`](platform-support/nuttx.md) | ✓ |  | ARMv7-A with NuttX, hardfloat
-`avr-none` | * |  | AVR; requires `-Zbuild-std=core` and `-Ctarget-cpu=...`
+[`avr-none`](platform-support/avr-none.md) | * |  | AVR; requires `-Zbuild-std=core` and `-Ctarget-cpu=...`
 `bpfeb-unknown-none` | * |  | BPF (big endian)
 `bpfel-unknown-none` | * |  | BPF (little endian)
 `csky-unknown-linux-gnuabiv2` | ✓ |  | C-SKY abiv2 Linux (little endian)