doc/go1.15: enumerate ELF-based OSes
doc/go1.15: enumerate ELF-based OSes

Users don't necessarily know if their OS is ELF-based.

For #37419.

Change-Id: I4a4256c5f5eb34211729e1311582bb0e210f1f8d
Reviewed-on: https://go-review.googlesource.com/c/go/+/238240
Reviewed-by: Than McIntosh <4b2922593166fc595a9b1a408f34f5d3817fe9d2@google.com>

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