Add to summary

Author: daltenty

src/doc/rustc/src/SUMMARY.md

@@ -72,6 +72,7 @@
     - [powerpc-unknown-linux-gnuspe](platform-support/powerpc-unknown-linux-gnuspe.md)
     - [powerpc-unknown-linux-muslspe](platform-support/powerpc-unknown-linux-muslspe.md)
     - [powerpc64-ibm-aix](platform-support/aix.md)
+    - [powerpc64le-unknown-linux-gnu](platform-support/powerpc64le-unknown-linux-gnu.md)
     - [powerpc64le-unknown-linux-musl](platform-support/powerpc64le-unknown-linux-musl.md)
     - [riscv32e\*-unknown-none-elf](platform-support/riscv32e-unknown-none-elf.md)
     - [riscv32i\*-unknown-none-elf](platform-support/riscv32-unknown-none-elf.md)