doc/go1.17: note deprecation of 'go get' for installing commands

Fixes #43684

Change-Id: I8982f6816c002c71e62f37a926c8543e34b8b785
Reviewed-on: https://go-review.googlesource.com/c/go/+/329549
Trust: Jay Conrod <[email protected]>
Reviewed-by: Bryan C. Mills <[email protected]>

Author: Jay Conrod

doc/go1.17.html

@@ -214,6 +214,16 @@ <h4 id="go-get"><code>go</code> <code>get</code></h4>
   <code>environment</code> for details.
 </p>
 
+<p><!-- golang.org/issue/43684 -->
+  <code>go</code> <code>get</code> prints a deprecation warning when installing
+  commands outside the main module (without the <code>-d</code> flag).
+  <code>go</code> <code>install</code> <code>cmd@version</code> should be used
+  instead to install a command at a specific version, using a suffix like
+  <code>@latest</code> or <code>@v1.2.3</code>. In Go 1.18, the <code>-d</code>
+  flag will always be enabled, and <code>go</code> <code>get</code> will only
+  be used to change dependencies in <code>go.mod</code>.
+</p>
+
 <h4 id="missing-go-directive"><code>go.mod</code> files missing <code>go</code> directives</h4>
 
 <p><!-- golang.org/issue/44976 -->