doc/go1.14: document RISC-V support
doc/go1.14: document RISC-V support

Fixes #36708
Updates #27532

Change-Id: I9e3bb92d15825e2c4a505e1aea41b2897f18e0ff
Reviewed-on: https://go-review.googlesource.com/c/go/+/216757
Reviewed-by: Joel Sing <4816dabf8db1bc6cac35b3a24cab2ff844b5b0c7@sing.id.au>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

CAFxX/go,golang/go,akutz/go,golang/go,akutz/go,cloudflare/go,CAFxX/go,akutz/go,nawawi/go,cloudflare/go,CAFxX/go,CAFxX/go,cloudflare/go,golang/go,akutz/go,nawawi/go,nawawi/go,nawawi/go,nawawi/go,cloudflare/go,akutz/go,nawawi/go,CAFxX/go,cloudflare/go,CAFxX/go,golang/go,golang/go,golang/go,CAFxX/go,akutz/go,cloudflare/go,nawawi/go,CAFxX/go,akutz/go,cloudflare/go,golang/go,golang/go,nawawi/go,cloudflare/go,akutz/go