Allow more pages to be indexed by search engine

- /index and /about were serious mistakes!
- /{install,upgrade}/*/*-overview.mdwn should be indexed for people
  searching for "install Tails from Windows" for example.
- /install/download can be indexed as it provide links to the different
  installation and upgrade scenarios.
- /install/download-iso shouldn't rather not be indexed as we don't want
  most people to use it without understanding that it's only for DVDs
  and VMs.

wiki/src/about.html

 [[!meta title="How Tails works"]]
 [[!meta stylesheet="about" rel="stylesheet" title=""]]
 [[!meta stylesheet="hide-breadcrumbs" rel="stylesheet" title=""]]
-[[!meta robots="noindex"]]
 
 <h1>Leave no trace on the computer</h1>
 

wiki/src/index.html

 [[!meta title="Home"]]
 [[!meta stylesheet="index" rel="stylesheet" title=""]]
 [[!meta stylesheet="hide-breadcrumbs" rel="stylesheet" title=""]]
-[[!meta robots="noindex"]]
 [[!meta google-site-verification="aGp--gO0AaDbtxshkcWaS0jY8WkOjYwUuBqRWzWHy6o"]]
 
 <script>

wiki/src/install/download.mdwn

 [[!meta title="Download and verify (for USB sticks)"]]
 
-[[!meta robots="noindex"]]
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="install/inc/stylesheets/assistant" rel="stylesheet" title=""]]
 [[!meta stylesheet="install/inc/stylesheets/download" rel="stylesheet" title=""]]

wiki/src/install/expert/usb-overview.html

 <div>[[!meta title="Install from Debian, Ubuntu, or Mint using the command line and GnuPG"]]</div>
 
-[[!meta robots="noindex"]]
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/assistant" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/overview" rel="stylesheet" title=""]]

wiki/src/install/linux/clone-overview.html

 <div>[[!meta title="Install from another Tails"]]</div>
 
-[[!meta robots="noindex"]]
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/assistant" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/overview" rel="stylesheet" title=""]]

wiki/src/install/linux/usb-overview.html

 <div>[[!meta title="Install from Linux"]]</div>
 
-[[!meta robots="noindex"]]
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/assistant" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/overview" rel="stylesheet" title=""]]

wiki/src/install/mac/clone-overview.html

 <div>[[!meta title="Install from another Tails"]]</div>
 
-[[!meta robots="noindex"]]
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/assistant" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/overview" rel="stylesheet" title=""]]

wiki/src/install/mac/usb-overview.html

 <div>[[!meta title="Install from macOS"]]</div>
 
-[[!meta robots="noindex"]]
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/assistant" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/overview" rel="stylesheet" title=""]]

wiki/src/install/win/clone-overview.html

 <div>[[!meta title="Install from another Tails"]]</div>
 
-[[!meta robots="noindex"]]
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/assistant" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/overview" rel="stylesheet" title=""]]

wiki/src/install/win/usb-overview.html

 <div>[[!meta title="Install from Windows"]]</div>
 
-[[!meta robots="noindex"]]
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/assistant" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/overview" rel="stylesheet" title=""]]

wiki/src/upgrade/clone-overview.html

 <div>[[!meta title="Manually upgrade by cloning from another Tails"]]</div>
 
-[[!meta robots="noindex"]]
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="install/inc/stylesheets/assistant" rel="stylesheet" title=""]]
 [[!meta stylesheet="install/inc/stylesheets/overview" rel="stylesheet" title=""]]

wiki/src/upgrade/linux-overview.html

 <div>[[!meta title="Manually upgrade from Linux"]]</div>
 
-[[!meta robots="noindex"]]
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="install/inc/stylesheets/assistant" rel="stylesheet" title=""]]
 [[!meta stylesheet="install/inc/stylesheets/overview" rel="stylesheet" title=""]]

wiki/src/upgrade/mac-overview.html

 <div>[[!meta title="Manually upgrade from macOS"]]</div>
 
-[[!meta robots="noindex"]]
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="install/inc/stylesheets/assistant" rel="stylesheet" title=""]]
 [[!meta stylesheet="install/inc/stylesheets/overview" rel="stylesheet" title=""]]

wiki/src/upgrade/tails-overview.html

 <div>[[!meta title="Manually upgrade from your Tails"]]</div>
 
-[[!meta robots="noindex"]]
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="install/inc/stylesheets/assistant" rel="stylesheet" title=""]]
 [[!meta stylesheet="install/inc/stylesheets/overview" rel="stylesheet" title=""]]

wiki/src/upgrade/win-overview.html

 <div>[[!meta title="Manually upgrade from Windows"]]</div>
 
-[[!meta robots="noindex"]]
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="install/inc/stylesheets/assistant" rel="stylesheet" title=""]]
 [[!meta stylesheet="install/inc/stylesheets/overview" rel="stylesheet" title=""]]