fix typos in fix restrain docs

* ID, group-ID are documented in :doc:`fix <fix>` command

* restrain = style name of this fix command

* one or more keyword/arg pairs may be appended

* keyword = *bond* or *angle* or *dihedral*

* keyword = *bond* or *lbound* or *angle* or *dihedral*

  .. parsed-literal::

         r0start = equilibrium bond distance at start of run (distance units)

         r0stop = equilibrium bond distance at end of run (optional) (distance units). If not

           specified it is assumed to be equal to r0start

       *lbond* args = atom1 atom2 Kstart Kstop r0start (r0stop)

       *lbound* args = atom1 atom2 Kstart Kstop r0start (r0stop)

         atom1,atom2 = IDs of 2 atoms in bond

         Kstart,Kstop = restraint coefficients at start/end of run (energy units)

         r0start = equilibrium bond distance at start of run (distance units)

.. code-block:: LAMMPS

   fix holdem all restrain bond 45 48 2000.0 2000.0 2.75

   fix holdem all restrain lbond 45 48 2000.0 2000.0 2.75

   fix holdem all restrain lbound 45 48 2000.0 2000.0 2.75

   fix holdem all restrain dihedral 1 2 3 4 2000.0 2000.0 120.0

   fix holdem all restrain bond 45 48 2000.0 2000.0 2.75 dihedral 1 2 3 4 2000.0 2000.0 120.0

   fix texas_holdem all restrain dihedral 1 2 3 4 0.0 2000.0 120.0 dihedral 1 2 3 5 0.0 2000.0 -120.0 dihedral 1 2 3 6 0.0 2000.0 0.0

----------

The *lbond* keyword applies a lower bound bond restraint to the specified atoms

The *lbound* keyword applies a lower bound bond restraint to the specified atoms

using the same functional form used by the :doc:`bond_style harmonic <bond_harmonic>` command if the distance between

the atoms is smaller than the equilibrium bond distance and 0 otherwise. The potential associated with

the restraint is