docs: fix typo in toolchains.md example code (#2970)

Added missing commas in `local toolchains` instructions

docs/toolchains.md

diff --git a/docs/toolchains.md b/docs/toolchains.md
index 57d43d2..be85a24 100644
--- a/docs/toolchains.md
+++ b/docs/toolchains.md
@@ -436,8 +436,8 @@
 )
 
 local_runtime_toolchains_repo = use_repo_rule(
-    "@rules_python//python/local_toolchains:repos.bzl"
-    "local_runtime_toolchains_repo"
+    "@rules_python//python/local_toolchains:repos.bzl",
+    "local_runtime_toolchains_repo",
     dev_dependency = True,
 )