Further root readme bump, factor `.clearing` content

In line with our move to `uv` and recent `nix` support update a bunch of
the summary content and factor out the order-control section to a new
`.piker.clearing` readme file with embedded todos therein.

README.rst

@@ -127,9 +127,9 @@ chart`` program::
 
     pikerd -l info --pdb
 
-the daemon does nothing until a ``pikers`-client (like `piker chart`) connects
-and requests some particular sub-system. for a chart connection
-``pikerd`` will spawn and manage at least,
+the daemon does nothing until a ``piker``-client (like ``piker
+chart``) connects and requests some particular sub-system. for
+a connecting chart ``pikerd`` will spawn and manage at least,
 
 - a data-feed daemon: ``datad`` which does all the work of comms with
   the backend provider (in this case the ``binance`` cex).