Document USES=go.

Sponsored by:	Absolight
Differential Revision:	https://reviews.freebsd.org/D6058

en_US.ISO8859-1/books/porters-handbook/uses/chapter.xml

@@ -978,6 +978,59 @@ USE_GNOME=	gnomemenus3:build intlhack</programlisting>
       information.</para>
   </sect1>
 
+  <sect1 xml:id="uses-go">
+    <title><literal>go</literal></title>
+
+    <para>Possible arguments: (none)</para>
+
+    <para>Sets default values and targets used to build
+      <application>Go</application> software.  A build-time dependency
+      on <package role="port">lang/go</package> is added.  The build
+      process is controlled by several variables:</para>
+
+    <variablelist>
+      <varlistentry>
+	<term><varname>GO_PKGNAME</varname></term>
+
+	<listitem>
+	  <para>The name of the <application>Go</application> package.
+	    This is the directory that will be created in
+	    <literal>GOPATH/src</literal>.  The default value is
+	    <varname>${PORTNAME}</varname>.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term><varname>GO_TARGET</varname></term>
+
+	<listitem>
+	  <para>The name of the packages to build.  The default
+	    value is <varname>${GO_PKGNAME}</varname>.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term><varname>CGO_CFLAGS</varname></term>
+
+	<listitem>
+	  <para>Additional <varname>CFLAGS</varname> values to be
+	    passed to the <application>C</application> compiler by
+	    <command>go</command>.</para>
+	</listitem>
+      </varlistentry>
+
+      <varlistentry>
+	<term><varname>CGO_LDFLAGS</varname></term>
+
+	<listitem>
+	  <para>Additional <varname>LDFLAGS</varname> values to be
+	    passed to the <application>C</application> compiler by
+	    <command>go</command>.</para>
+	</listitem>
+      </varlistentry>
+    </variablelist>
+  </sect1>
+
   <sect1 xml:id="uses-gperf">
     <title><literal>gperf</literal></title>