chore: update README.md for v0.21.0 (#455)

Automated update of `README.md` for release v0.21.0

This pull request was created by
[cgrindel/gha_create_release](https://github.com/cgrindel/gha_create_release).

Co-authored-by: cgrindel <cgrindel@users.noreply.github.com>

README.md

@@ -35,7 +35,7 @@ how-to links above and review the [the generated documentation](/doc/).
 
 <!-- BEGIN MODULE SNIPPET -->
 ```python
-bazel_dep(name = "cgrindel_bazel_starlib", version = "0.20.2")
+bazel_dep(name = "cgrindel_bazel_starlib", version = "0.21.0")
 ```
 <!-- END MODULE SNIPPET -->
 
@@ -47,9 +47,9 @@ load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 
 http_archive(
     name = "cgrindel_bazel_starlib",
-    sha256 = "1749e14037e67cfeaf28b71334ef4ade7727edaafc890f8cee7648939eae77d4",
+    sha256 = "c088657482e86888c9f46f535bdbaf71eaeb35ff9db04912a4ecdccf94cd16d5",
     urls = [
-        "https://github.com/cgrindel/bazel-starlib/releases/download/v0.20.2/bazel-starlib.v0.20.2.tar.gz",
+        "https://github.com/cgrindel/bazel-starlib/releases/download/v0.21.0/bazel-starlib.v0.21.0.tar.gz",
     ],
 )