_content: update A Tour of Go description

Fixes golang/go#59167

Change-Id: Ib433ac314e1ad58b6f0a74ca346e49e53834df95
Reviewed-on: https://go-review.googlesource.com/c/website/+/478395
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Jamal Carvalho <jamal@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

_content/blog/tour.md

@@ -17,9 +17,10 @@ The tour is hands-on, demonstrating the language through code samples that you c
 compile, and run from the tour itself.
 (The technology behind the [Go Playground](/doc/play/) does the work.)
 
-The tour has three sections. The first section covers basic syntax and data structures;
+The tour has four sections. The first section covers basic syntax and data structures;
 the second discusses methods and interfaces;
-and the third introduces Go's concurrency primitives.
+the third is about Generics;
+and the fourth introduces Go's concurrency primitives.
 Each section concludes with a few exercises so you can practice what you've learned.
 
 So, what are you waiting for? [Get started now!](/tour/)

_content/doc/index.html

@@ -58,9 +58,9 @@ to build and test packages.
 
 <h3 id="go_tour"><a href="/tour/">A Tour of Go</a></h3>
 <p>
-An interactive introduction to Go in three sections.
+An interactive introduction to Go in four sections.
 The first section covers basic syntax and data structures; the second discusses
-methods and interfaces; and the third introduces Go's concurrency primitives.
+methods and interfaces; the third is about Generics; and the fourth introduces Go's concurrency primitives.
 Each section concludes with a few exercises so you can practice what you've
 learned. You can <a href="/tour/">take the tour online</a> or install it locally with:
 </p>

_content/learn/quickstart.yaml

@@ -4,7 +4,7 @@
     cta: View documentation
     url: /doc/
   - title: Tour of Go
-    content: An interactive introduction to Go in three sections. Each section
+    content: An interactive introduction to Go in four sections. Each section
       concludes with a few exercises so you can practice what you've learned.
     cta: Take a tour
     url: /tour/