Add examples of how to generate and validate generate_codeowners

See #13 (comment)

README.md

@@ -90,3 +90,60 @@ sh_test(
     ],
 )
 ```
+
+## Automation tip: Automatically populate the `generate_codeowners`
+
+To automatically set all `codeowners` as owners in a `generate_codeowners`, the following script that utilizes `bazel query` and [`buildozer`](https://github.com/bazelbuild/buildtools/tree/master/buildozer) can be used.
+
+```bash
+#!/usr/bin/env bash
+
+# target to the generate_codeowners, eg "//.github:gen_codeowners"
+readonly target=$1
+
+readonly BAZEL=$(which bazel)
+readonly BUILDOZER=$(which buildozer)
+
+readonly new_owners=$(
+    # Query for all codeowners() rules (anchor at the front to avoid match on generate_codeowners rule)
+    $BAZEL query --output=label 'kind("^codeowners rule", //...)' |
+    # Print the length of each label at the front of the line
+    awk '{ print length, $0 }' |
+    # Sort shortest-first, so that the root //:OWNERS ends up first in CODEOWNERS
+    sort -n -s |
+    # 43 label -> "label"
+    awk '{ print "\x22" $2 "\x22" }' |
+    # comma-separated
+    tr '\n' ','
+)
+
+readonly command="set owners [${new_owners}]|${target}"
+
+echo "$command" | $BUILDOZER -f -
+```
+
+## Automation tip: Verify that all codeowners are transiently depended on a `generate_codeowners`
+
+To verify that all `codeowners` are targeted by a `generate_codeowners`, a script like the one below can be used.
+
+```bash
+#!/usr/bin/env bash
+
+# target to the generate_codeowners, eg "//.github:gen_codeowners"
+readonly target=$1
+
+readonly TEEFILE=$(mktemp)
+readonly BAZEL=$(which bazel)
+
+$BAZEL query "kind(codeowners, //...) except deps(${target})" 2>&1 | tee "$TEEFILE" | grep "Empty results"
+EXIT=$?
+
+if [ "$EXIT" -eq 1 ]; then
+    cat "$TEEFILE"
+    echo "--> All codeowners rules must be depended on by ${target}"
+    echo "--> Add the codeowners as a dependency, or delete the target"
+    exit 1
+fi
+
+exit 0
+```