_content/security: Added Best Practices to index

Added a link to the Security Best Practices guide to the go.dev/security page.

Change-Id: Ie5282d45f574ea2ea6cb4c501140d7cc27b415e7
Reviewed-on: https://go-review.googlesource.com/c/website/+/509715
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Brandon Kessler <bkessler@google.com>
Reviewed-by: Julie Qiu <julieqiu@google.com>
Auto-Submit: Julie Qiu <julieqiu@google.com>
Run-TryBot: Julie Qiu <julieqiu@google.com>

_content/security/index.md

@@ -6,6 +6,8 @@ layout: article
 This page provides resources for Go developers to improve security for their
 projects.
 
+(See also: [Security Best Practices for Go Developers](https://go.dev/security/best-practices).)
+
 ## Find and fix known vulnerabilities
 
 Go’s vulnerability detection aims to provide low-noise, reliable tools for
@@ -14,7 +16,6 @@ For an overview, start at [this summary and FAQ page](https://go.dev/security/vu
 about Go’s vulnerability management architecture. For an applied approach,
 explore the tools below.
 
-
 ### Scan code for vulnerabilities with govulncheck
 
 Developers can use the govulncheck tool to determine whether any known