static/shared: update footer with link to pkg.go.dev/about

Video:https://drive.google.com/file/d/10dfZQgpEh2590taRXw6lYd0pcbhvg6u1/view?usp=sharing

Change-Id: Ifc6323b9f5fc1560bd0cccc99a44b3fe0e0ba189
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/443115
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
Run-TryBot: Jamal Carvalho <jamal@golang.org>
Reviewed-by: Jamal Carvalho <jamal@golang.org>
diff --git a/static/shared/footer/footer.tmpl b/static/shared/footer/footer.tmpl
index 4f48531..032d487 100644
--- a/static/shared/footer/footer.tmpl
+++ b/static/shared/footer/footer.tmpl
@@ -50,6 +50,9 @@
         <a href="/std" class="go-Footer-link" data-gtmc="footer link">
           Standard Library
         </a>
+        <a href="https://pkg.go.dev/about" class="go-Footer-link" data-gtmc="footer link">
+          About Go Packages
+        </a>
       </div>
       <div class="go-Footer-linkColumn">
         <a href="https://go.dev/project" class="go-Footer-link go-Footer-link--primary"