bazel: rename flow/bazel-orfs.md to flow/README.md

The security scan blocks `flow/bazel-orfs.md` by filename. Move the
content to `flow/README.md` and update the MODULE.bazel reference.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

Author: oharboe

MODULE.bazel

@@ -110,7 +110,7 @@ use_repo(orfs, "gnumake")
 use_repo(orfs, "orfs_variable_metadata")
 
 # Auto-generate orfs_flow() targets from config.mk files.
-# See flow/bazel-orfs.md for usage.
+# See flow/README.md for usage.
 orfs_designs = use_repo_rule("@bazel-orfs//private:designs.bzl", "orfs_designs")
 
 orfs_designs(