Warn about dragons in the Bazel include path

#837 has caused a couple of
disappointments for PR authors, so I'm hoping this comment can save them
some time, or even help them towards finding a complete solution for the
problem.

bazel/glog.bzl

@@ -201,6 +201,12 @@ def glog_library(namespace = "google", with_gflags = 1, **kwargs):
             ":stl_logging_h",
             ":vlog_is_on_h",
         ],
+        # https://github.com/google/glog/issues/837: Replacing
+        # `strip_include_prefix` with `includes` would avoid spamming
+        # downstream projects with compiler warnings, but would also leak
+        # private headers like stacktrace.h. I suspect the only way to avoid
+        # this is to refactor the project including the CMake build, so that
+        # the private headers are in a glog_internal subdirectory.
         strip_include_prefix = "src",
         defines = final_lib_defines,
         copts = final_lib_copts,