Fix autosectionlabel warnings

[moorepants]

I need to update all of the following instances of :ref: and update the README with notes on the prefix:

$ grep -r ":ref:" --include=*.rst
noncontributing.rst:(See Sec. :ref:`Contributing and Noncontributing Forces`), but often we are
motion.rst:In :ref:`Holonomic Constraints`, we discussed constraints on the configuration
motion.rst:Recall from :ref:`Solving Linear Systems` that the Jacobian is a simple way
README.rst:   :ref:`Chapter`
README.rst:   :ref:`Section`
README.rst:   :ref:`Subsection`
README.rst:   :ref:`Subsubsection`
configuration.rst:   See :ref:`collision` for more information.
configuration.rst:numerically. In :ref:`Equations of Motion with Holonomic Constraints` we will
configuration.rst:those variables using the technique shown in :ref:`Solving Linear Systems`.
configuration.rst::ref:`Solving Holonomic Constraints`, but once done only the independent
nonholonomic-eom.rst:In chapters, :ref:`Holonomic Constraints` and :ref:`Nonholonomic Constraints`,
nonholonomic-eom.rst:dependent generalized speeds (see Sec. :ref:`Snakeboard`). We have shown that
nonholonomic-eom.rst:Let's revisit the snakeboard example (see Sec. :ref:`Snakeboard`) and develop
angular.rst::ref:`Successive Orientations` to find the angular kinematics of a set of
angular.rst:In Ch. :ref:`Orientation of Reference Frames` we learned that reference frames
angular.rst::ref:`Direction Cosine Matrices`):
angular.rst:return to the product rule in Section :ref:`Product Rule` and first express
angular.rst:orientations (Sec. :ref:`Successive Orientations`), there is a relationship
angular.rst:angular velocities explained in Sec. :ref:`Addition of Angular Velocity` does
vectors.rst:   Reread the :ref:`Vector Functions` section and answer the following
lagrange.rst:forces, see :ref:`Unconstrained Equations of Motion`.  A large part of Kane's
lagrange.rst:derivatives. See :ref:`Energy and Power` for the definition of kinetic energy.
lagrange.rst:This example is largely the same as the example in :ref:`Body Fixed
lagrange.rst:Recall from :ref:`Energy and Power` that `conservative forces`_, can be
lagrange.rst:the system introduced in :ref:`Example of Kane's Equations`. The description of
lagrange.rst:in :ref:`Equations of Motion with Nonholonomic Constraints`.
lagrange.rst::ref:`Exposing Noncontributing Forces`. First the constraints are omitted, then
lagrange.rst:\hat{n}_z`. By using the :ref:`Velocity Two Point Theorem`, the following
lagrange.rst:better to use a differential algebraic solver, as discussed in :ref:`Equations
tmt.rst:Let us return once again to the holonomic system introduced in :ref:`Example of
tmt.rst:numbers we used in :ref:`Numerical Evaluation`. The input values were:
generalized-forces.rst:velocity, recall the :ref:`Chaplygin Sleigh` velocity equations where
eom.rst::ref:`Solving Linear Systems`).
holonomic-eom.rst::ref:`Equations of Motion with Nonholonomic Constraints`.
holonomic-eom.rst::ref:`Four-bar Linkage`. We will now make :math:`P_2` and :math:`P_3`
simulation.rst::ref:`Evaluating Symbolic Expressions` we introduced the SymPy function
orientation.rst:technique for the successive simple orientations shown in :ref:`Successive
orientation.rst:  orientation from the angular velocity (see :ref:`Angular Kinematics`).
mass.rst:if the orientation is defined (demonstrated above in :ref:`Dyadics`):
energy.rst::ref:`Collision`. We will actuate the jumper using only a torque acting between