README: split into sections, reformat for github.io

Split the rather large README into smaller sections with a pitch and
a ToC at the top.

Move the sections into docs/ so that Github Pages can read them.

'make doc' produces a local HTML tree.

Update the kernel bugs and gotchas list.

Add some information that has been accumulating in Github comments.

Remove information about bugs in kernels earlier than 4.14.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

docs/index.md

@@ -0,0 +1,73 @@
+BEES
+====
+
+Best-Effort Extent-Same, a btrfs deduplication agent.
+
+About bees
+----------
+
+bees is a block-oriented userspace deduplication agent designed for large
+btrfs filesystems.  It is an offline dedupe combined with an incremental
+data scan capability to minimize time data spends on disk from write
+to dedupe.
+
+Strengths
+---------
+
+ * Space-efficient hash table and matching algorithms - can use as little as 1 GB hash table per 10 TB unique data (0.1GB/TB)
+ * Incremental realtime dedupe of new data using btrfs tree search
+ * Works with btrfs compression - dedupe any combination of compressed and uncompressed files
+ * Works around btrfs filesystem structure to free more disk space
+ * Persistent hash table for rapid restart after shutdown
+ * Whole-filesystem dedupe - including snapshots
+ * Constant hash table size - no increased RAM usage if data set becomes larger
+ * Works on live data - no scheduled downtime required
+ * Automatic self-throttling based on system load
+
+Weaknesses
+----------
+
+ * Whole-filesystem dedupe - has no include/exclude filters, does not accept file lists
+ * Runs continuously as a daemon - no quick start/stop
+ * Requires root privilege (or `CAP_SYS_ADMIN`)
+ * First run may require temporary disk space for extent reorganization
+ * [First run may increase metadata space usage if many snapshots exist](gotchas.md)
+ * Constant hash table size - no decreased RAM usage if data set becomes smaller
+ * btrfs only
+
+Installation and Usage
+----------------------
+
+ * [Installation](install.md)
+ * [Configuration](config.md)
+ * [Running](running.md)
+ * [Command Line Options](options.md)
+
+Recommended Reading
+-------------------
+
+ * [bees Gotchas](gotchas.md)
+ * [btrfs kernel bugs](btrfs-kernel.md)
+ * [bees vs. other btrfs features](btrfs-other.md)
+
+More Information
+----------------
+
+ * [How bees works](how-it-works.md)
+ * [Missing bees features](missing.md)
+
+Bug Reports and Contributions
+-----------------------------
+
+Email bug reports and patches to Zygo Blaxell <bees@furryterror.org>.
+
+You can also use Github:
+
+        https://github.com/Zygo/bees
+
+Copyright & License
+-------------------
+
+Copyright 2015-2018 Zygo Blaxell <bees@furryterror.org>.
+
+GPL (version 3 or later).