btrfs-progs: docs: restyle the landing page

Add an introductory paragraph with most important links, put TOC
listings to columns.

[ci skip]

Signed-off-by: David Sterba <dsterba@suse.com>

Documentation/Status.rst

@@ -388,7 +388,7 @@ are unaffected by the zoned device constraints.
 
 
 Details that do not fit the table
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+---------------------------------
 
 Defrag
 ^^^^^^

Documentation/_static/style.css

@@ -35,3 +35,12 @@
 .statusincompat {
 	color: goldenrod;
 };
+
+table.main-table {
+	border: 1px;
+	width: 100%;
+}
+
+td.main-table-col {
+	width: 33%;
+}

Documentation/index.rst

@@ -3,6 +3,17 @@
 Welcome to BTRFS documentation!
 ===============================
 
+BTRFS is a modern copy on write (COW) filesystem for Linux aimed at
+implementing advanced features while also focusing on fault tolerance, repair
+and easy administration. You can read more about the features in the
+:doc:`introduction<Introduction>` or choose from the pages below. Documentation
+for for command line tools :doc:`btrfs`, :doc:`mkfs.btrfs` and others
+is in the :doc:`manual pages<man-index>`.
+
+.. raw:: html
+
+   <table><tr><td class="main-table-col">
+
 .. toctree::
    :maxdepth: 1
    :caption: Overview
@@ -20,9 +31,13 @@ Welcome to BTRFS documentation!
    INSTALL
    Source-repositories
 
+.. raw:: html
+
+   </td><td class="main-table-col">
+
 .. toctree::
    :maxdepth: 1
-   :caption: Features:
+   :caption: Features
 
    Common-features
    Custom-ioctls
@@ -48,6 +63,10 @@ Welcome to BTRFS documentation!
    Volume-management
    Zoned-mode
 
+.. raw:: html
+
+   </td><td class="main-table-col">
+
 .. toctree::
    :maxdepth: 1
    :caption: Developer documentation
@@ -64,6 +83,19 @@ Welcome to BTRFS documentation!
    dev/ReleaseChecklist
    btrfs-ioctl
 
+
+.. raw:: html
+
+   </td></tr></table>
+
+.. raw:: html
+
+   <hr />
+
+This documentation is still work in progress, not everything from the original
+wiki https://btrfs.wiki.kernel.org has been moved here. Below are starting points
+for missing contents.
+
 .. toctree::
    :maxdepth: 1
    :caption: TODO