Add --index to install man page.

src/doc/man/cargo-install.adoc

@@ -135,6 +135,8 @@ available.
 
 include::options-registry.adoc[]
 
+include::options-index.adoc[]
+
 include::options-features.adoc[]
 
 === Compilation Options

src/doc/man/generated/cargo-install.html

@@ -197,6 +197,10 @@ <h3 id="cargo_install_install_options">Install Options</h3>
 If not specified, the default registry is used, which is defined by the
 <code>registry.default</code> config key which defaults to <code>crates-io</code>.</p>
 </dd>
+<dt class="hdlist1"><strong>--index</strong> <em>INDEX</em></dt>
+<dd>
+<p>The URL of the registry index to use.</p>
+</dd>
 </dl>
 </div>
 </div>

src/etc/man/cargo-install.1

@@ -2,12 +2,12 @@
 .\"     Title: cargo-install
 .\"    Author: [see the "AUTHOR(S)" section]
 .\" Generator: Asciidoctor 2.0.10
-.\"      Date: 2020-02-06
+.\"      Date: 2020-06-14
 .\"    Manual: \ \&
 .\"    Source: \ \&
 .\"  Language: English
 .\"
-.TH "CARGO\-INSTALL" "1" "2020-02-06" "\ \&" "\ \&"
+.TH "CARGO\-INSTALL" "1" "2020-06-14" "\ \&" "\ \&"
 .ie \n(.g .ds Aq \(aq
 .el       .ds Aq '
 .ss \n[.ss] 0
@@ -293,6 +293,11 @@ Name of the registry to use. Registry names are defined in \c
 If not specified, the default registry is used, which is defined by the
 \fBregistry.default\fP config key which defaults to \fBcrates\-io\fP.
 .RE
+.sp
+\fB\-\-index\fP \fIINDEX\fP
+.RS 4
+The URL of the registry index to use.
+.RE
 .SS "Feature Selection"
 .sp
 The feature flags allow you to control the enabled features for the "current"