Create docs/ folder and move container_image documentation there.

This documentation is now generated from sources rather than hand-maintained in markdown/HTML.

Move the existing starlark target there, and check in the generated output.
Uses generated_file_test since that prints the bazel run command to accept the new file,
making this workflow easy for novice contributors to follow.

Also don't make users install the stardoc repository anymore, now that they don't load() from this BUILD file they shouldn't need it.

Author: alexeagle

README.md

@@ -516,3 +516,14 @@ load("@io_bazel_rules_kotlin//kotlin:kotlin.bzl", "kotlin_repositories", "kt_reg
 kotlin_repositories()
 
 kt_register_toolchains()
+
+# For API doc generation
+http_archive(
+    name = "io_bazel_stardoc",
+    patches = [],
+    sha256 = "f89bda7b6b696c777b5cf0ba66c80d5aa97a6701977d43789a9aee319eef71e8",
+    strip_prefix = "stardoc-d93ee5347e2d9c225ad315094507e018364d5a67",
+    urls = [
+        "https://github.com/bazelbuild/stardoc/archive/d93ee5347e2d9c225ad315094507e018364d5a67.tar.gz",
+    ],
+)

WORKSPACE

@@ -13,7 +13,6 @@
 # limitations under the License.
 
 load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
-load("@io_bazel_stardoc//stardoc:stardoc.bzl", "stardoc")
 
 package(default_visibility = ["//visibility:public"])
 
@@ -192,13 +191,6 @@ bzl_library(
     ],
 )
 
-stardoc(
-    name = "image_doc",
-    out = "image.md",
-    input = ":image.bzl",
-    deps = [":image"],
-)
-
 bzl_library(
     name = "import",
     srcs = ["import.bzl"],