README: protobuf dependency example does not build

[johnsonj]

What version of rules_go are you using?

v0.22.4

What version of gazelle are you using?

v0.20.0

What version of Bazel are you using?

3.0.0

Does this issue reproduce with the latest releases of all the above?

Yes

What operating system and processor architecture are you using?

Ubuntu 18.04, Linux studio 4.19.84-microsoft-standard #1 SMP Wed Nov 13 11:44:37 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

Any other potentially useful information about your toolchain?

Running under Windows 10 - WSL 2

What did you do?

Copied proto dependency example from README:

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

http_archive(
    name = "com_google_protobuf",
    sha256 = "9748c0d90e54ea09e5e75fb7fac16edce15d2028d4356f32211cfa3c0e956564",
    urls = ["https://github.com/protocolbuffers/protobuf/archive/v3.11.4.zip"],
)

load("@com_google_protobuf//:protobuf_deps.bzl", "protobuf_deps")

protobuf_deps()

What did you expect to see?

Build succeeds

What did you see instead?

$ make gazelle
bazel run //:gazelle
ERROR: error loading package '': Every .bzl file must have a corresponding package, but '@com_google_protobuf//:protobuf_deps.bzl' does not have one. Please create a BUILD file in the same or any parent directory. Note that this BUILD file does not need to do anything except exist.
INFO: Elapsed time: 0.454s
INFO: 0 processes.
FAILED: Build did NOT complete successfully (0 packages loaded)
FAILED: Build did NOT complete successfully (0 packages loaded)
Makefile:17: recipe for target 'gazelle' failed
make: *** [gazelle] Error 1