Update README.md to reflect Cloud Run functions rebrand (#1509)

Author: jama22

functions/README.md

@@ -1,6 +1,13 @@
 # Ruby Cloud Functions samples
 
-This directory contains the Ruby samples for Cloud Functions.
+This directory contains the Ruby samples for Cloud Run Functions.
+
+[Cloud Run functions](https://cloud.google.com/functions/docs/concepts/overview) is a lightweight, event-based, asynchronous compute solution that allows you to create small, single-purpose functions that respond to Cloud events without the need to manage a server or a runtime environment.
+
+There are two versions of Cloud Run functions:
+
+* **Cloud Run functions**, formerly known as Cloud Functions (2nd gen), which deploys your function as services on Cloud Run, allowing you to trigger them using Eventarc and Pub/Sub. Cloud Run functions are created using `gcloud functions` or `gcloud run`. Samples for Cloud Run functions can be found in the [`functions/v2`](v2/) folder.
+* **Cloud Run functions (1st gen)**, formerly known as Cloud Functions (1st gen), the original version of functions with limited event triggers and configurability. Cloud Run functions (1st gen) are created using `gcloud functions --no-gen2`. Samples for Cloud Run functions (1st generation) can be found in the current `functions/` folder.
 
 Samples are organized one region tag (i.e. one sample) per file, where the file
 paths (directories and file names) match the region tags. For example, the