doc/go1.10: document that Go 1.11 will remove Windows XP support
doc/go1.10: document that Go 1.11 will remove Windows XP support

Fixes #23380.

Change-Id: Ia9a086eada21b5561f110833afcf93e542a04407
Reviewed-on: https://go-review.googlesource.com/87175
Run-TryBot: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Reviewed-by: Alex Brainman <54ba58c8441b5eff861de6b4e5ee46baf086b142@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

cloudflare/go,christopher-henderson/Go,golang/go,golang/go,akutz/go,golang/go,josharian/go,cloudflare/go,CAFxX/go,akutz/go,CAFxX/go,codestation/go,cloudflare/go,Cofyc/go,CAFxX/go,codestation/go,josharian/go,akutz/go,nawawi/go,Cofyc/go,golang/go,nawawi/go,josharian/go,nawawi/go,CAFxX/go,nawawi/go,golang/go,codestation/go,nawawi/go,josharian/go,golang/go,CAFxX/go,akutz/go,CAFxX/go,akutz/go,Cofyc/go,cloudflare/go,cloudflare/go,josharian/go,CAFxX/go,cloudflare/go,Cofyc/go,Cofyc/go,cloudflare/go,nawawi/go,codestation/go,akutz/go,codestation/go,nawawi/go,josharian/go,codestation/go,josharian/go,codestation/go,Cofyc/go,Cofyc/go,golang/go,nawawi/go,akutz/go,akutz/go,golang/go,codestation/go,josharian/go,CAFxX/go,cloudflare/go,Cofyc/go