Work on expanding documentation for layouts

docs/layouts.rst

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+Layouts
+============
+
+kitty has the ability to define its own windows that can be tiled next to each
+other in arbitrary arrangements, based on *Layouts*, see below for examples:
+
+
+.. figure:: screenshots/screenshot.png
+    :alt: Screenshot, showing three programs in the 'Tall' layout
+    :align: center
+    :scale: 100%
+
+    Screenshot, showing vim, tig and git running in |kitty| with the 'Tall' layout
+
+
+.. figure:: screenshots/splits.png
+    :alt: Screenshot, showing windows in the 'Splits' layout
+    :align: center
+    :scale: 100%
+
+    Screenshot, showing windows with arbitrary arrangement in the 'Splits'
+    layout
+
+
+You can resize windows inside layouts. Press :sc:`start_resizing_window` (also :kbd:`⌘+r` on macOS) to
+enter resizing mode and follow the on-screen instructions.  In a given window
+layout only some operations may be possible for a particular window. For
+example, in the Tall layout you can make the first window wider/narrower, but
+not taller/shorter. Note that what you are resizing is actually not a window,
+but a row/column in the layout, all windows in that row/column will be resized.
+
+You can also define shortcuts in :file:`kitty.conf` to make the active window
+wider, narrower, taller, or shorter by mapping to the ``resize_window``
+action, for example::
+
+   map ctrl+left resize_window narrower
+   map ctrl+right resize_window wider
+   map ctrl+up resize_window taller
+   map ctrl+down resize_window shorter 3
+
+The ``resize_window`` action has a second, optional argument to control
+the resizing increment (a positive integer that defaults to 1).
+
+
+Some layouts take options to control their behavior. For example, the ``fat``
+and ``tall`` layouts accept the ``bias`` and ``full_size`` options to control
+how the available space is split up.
+To specify the option, in :opt:`kitty.conf <enabled_layouts>` use::
+
+    enabled_layouts tall:bias=70;full_size=2
+
+This will have ``2`` instead of a single tall window, that occupy ``70%``
+instead of ``50%`` of available width. ``bias`` can be any number between 10
+and 90.
+
+Writing a new layout only requires about a hundred lines of code, so if there
+is some layout you want, take a look at `layout.py
+<https://github.com/kovidgoyal/kitty/blob/master/kitty/layout.py>`_  and submit
+a pull request!