docs: renumber headings

It's generally frowned upon to have multiple H1 headings in HTML4. So
let's make sure each article has a primary heading for the article, and
that that heading is the title that is used in the sidebar.

While we're at it, let's update the title in the articles to match the
title from the sidebar as well.

Signed-off-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
diff --git a/docs/install.html b/docs/install.html
index 036e1d8..4730a0c 100644
--- a/docs/install.html
+++ b/docs/install.html
@@ -31,9 +31,9 @@
 </ol>
 
 
-<h1 id="prereq-general">1. Prerequisites for building</h1>
+<h2 id="prereq-general">1. Prerequisites for building</h2>
 
-<h2>1.1 General</h2>
+<h3>1.1 General</h3>
 
 <p>
 Build system.
@@ -114,7 +114,7 @@
   ... # others
 </pre>
 
-<h1 id="meson">2. Building with meson</h1>
+<h2 id="meson">2. Building with meson</h2>
 
 <p>
 Meson is the latest build system in mesa, it is currently able to build for
@@ -134,7 +134,7 @@
 for more information
 </p>
 
-<h1 id="autoconf">3. Building with autoconf (Linux/Unix/X11)</h1>
+<h2 id="autoconf">3. Building with autoconf (Linux/Unix/X11)</h2>
 
 <p>
   Autoconf support was removed in Mesa 19.1.0. Please use meson instead.
@@ -142,7 +142,7 @@
 
 
 
-<h1 id="scons">4. Building with SCons (Windows/Linux)</h1>
+<h2 id="scons">4. Building with SCons (Windows/Linux)</h2>
 
 <p>
 To build Mesa with SCons on Linux or Windows do
@@ -178,7 +178,7 @@
 
 
 
-<h1 id="android">5. Building with AOSP (Android)</h1>
+<h2 id="android">5. Building with AOSP (Android)</h2>
 
 <p>
 Currently one can build Mesa for Android as part of the AOSP project, yet
@@ -197,7 +197,7 @@
 </p>
 
 
-<h1 id="libs">6. Library Information</h1>
+<h2 id="libs">6. Library Information</h2>
 
 <p>
 When compilation has finished, look in the top-level <code>lib/</code>
@@ -235,7 +235,7 @@
 </p>
 
 
-<h1 id="pkg-config">7. Building OpenGL programs with pkg-config</h1>
+<h2 id="pkg-config">7. Building OpenGL programs with pkg-config</h2>
 
 <p>
 Running <code>ninja install</code> will install package configuration files