docs: add sphinx index.rst, improve headers

docs/about.rst

@@ -1,11 +1,33 @@
 .. -*- coding: utf-8-with-signature -*-
 
+**********************
 Welcome to Tahoe-LAFS!
-======================
+**********************
+
+What is Tahoe-LAFS?
+===================
 
 Welcome to Tahoe-LAFS_, the first decentralized storage system with
 *provider-independent security*.
 
+Tahoe-LAFS is a system that helps you to store files. You run a client
+program on your computer, which talks to one or more storage servers on other
+computers. When you tell your client to store a file, it will encrypt that
+file, encode it into multiple pieces, then spread those pieces out among
+multiple servers. The pieces are all encrypted and protected against
+modifications. Later, when you ask your client to retrieve the file, it will
+find the necessary pieces, make sure they haven't been corrupted, reassemble
+them, and decrypt the result.
+
+The client creates more pieces (or "shares") than it will eventually need, so
+even if some of the servers fail, you can still get your data back. Corrupt
+shares are detected and ignored, so the system can tolerate server-side
+hard-drive errors. All files are encrypted (with a unique key) before
+uploading, so even a malicious server operator cannot read your data. The
+only thing you ask of the servers is that they can (usually) provide the
+shares when you ask for them: you aren't relying upon them for
+confidentiality, integrity, or absolute availability.
+
 .. _Tahoe-LAFS: https://tahoe-lafs.org
 
 What is "provider-independent security"?

docs/convergence-secret.rst

@@ -1,5 +1,9 @@
 .. -*- coding: utf-8-with-signature -*-
 
+**********************
+The Convergence Secret
+**********************
+
 What Is It?
 -----------
 

docs/index.rst

@@ -3,15 +3,48 @@
    You can adapt this file completely to your liking, but it should at least
    contain the root `toctree` directive.
 
-Welcome to Tahoe-LAFS's documentation!
+Tahoe-LAFS
-======================================
+==========
 
 Contents:
 
 .. toctree::
    :maxdepth: 2
 
+   about
+   INSTALL
+   running
+   configuration
+   architecture
 
+   frontends/CLI
+   frontends/webapi
+   frontends/FTP-and-SFTP
+   frontends/drop-upload
+   frontends/download-status
+
+   known_issues
+
+   helper
+   convergence-secret
+   garbage-collection
+
+   backdoors
+   donations
+   cautions
+   write_coordination
+   backupdb
+
+   nodekeys
+   performance
+   logging
+   stats
+
+   desert-island
+   debian
+   windows
+   OS-X
+   build/build-pyOpenSSL
 
 Indices and tables
 ==================

docs/running.rst

@@ -1,12 +1,12 @@
 .. -*- coding: utf-8-with-signature-unix; fill-column: 73; -*-
 .. -*- indent-tabs-mode: nil -*-
 
-=====================
+*********************
 How To Run Tahoe-LAFS
-=====================
+*********************
 
-Intro
+Introduction
-=====
+============
 
 This is how to run a Tahoe-LAFS client or a complete Tahoe-LAFS grid.
 First you have to install the Tahoe-LAFS software, as documented in