_content/doc/go1.26: preannounce the removal of big-endian linux/ppc64 port

For golang/go#76244.
For golang/go#75005.

Change-Id: I4ec783a32d7709f1e952b19807fec0ca7c530434
Reviewed-on: https://go-review.googlesource.com/c/website/+/729441
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: David Chase <drchase@google.com>
Reviewed-by: David Chase <drchase@google.com>

_content/doc/go1.26.md

diff --git a/_content/doc/go1.26.md b/_content/doc/go1.26.md
index 044dad1..87f6510 100644
--- a/_content/doc/go1.26.md
+++ b/_content/doc/go1.26.md
@@ -636,5 +636,13 @@
 
 As [announced](/doc/go1.25#windows) in the Go 1.25 release notes, the [broken](/doc/go1.24#windows) 32-bit windows/arm port (`GOOS=windows` `GOARCH=arm`) is removed.
 
+### PowerPC
+
+<!-- go.dev/issue/76244 -->
+
+Go 1.26 is the last release that supports the big-endian 64-bit PowerPC
+port on Linux (`GOOS=linux` `GOARCH=ppc64`).
+The port will be removed in Go 1.27.
+
 [laelf-20250521]: https://github.com/loongson/la-abi-specs/blob/v2.40/laelf.adoc
 [rfc 9180]: https://rfc-editor.org/rfc/rfc9180.html