update link and formatting of install via git page in manual.

Once the command completes, your directory will contain the same files

as if you unpacked a current LAMMPS tarball, with the exception, that

the HTML documentation files are not included.  They can be fetched

from the LAMMPS website by typing "make fetch" in the doc directory.

from the LAMMPS website by typing ``make fetch`` in the doc directory.

Or they can be generated from the content provided in doc/src by

typing "make html" from the doc directory.

typing ``make html`` from the doc directory.

After initial cloning, as bug fixes and new features are added to

LAMMPS, as listed on :doc:`this page <Errors_bugs>`, you can stay

If you want to access a particular previous release version of LAMMPS,

you can instead "check out" any version with a published tag. See the

output of "git tag -l" for the list of tags.  The git command to do

output of ``git tag -l`` for the list of tags.  The git command to do

this is as follows.

.. code-block:: bash

   $ git checkout tagID

Stable versions and what tagID to use for a particular stable version

are discussed on :doc:`this page <Errors_bugs>`.  Note that this command

will print some warnings, because in order to get back to the latest

revision and to be able to update with "git pull" again, you first

will need to first type "git checkout unstable" (or check out any

other desired branch).

Once you have updated your local files with a "git pull" (or "git

checkout"), you still need to re-build LAMMPS if any source files have

are discussed on `this page <https://lammps.sandia.gov/bug.html#version>`_.

Note that this command will print some warnings, because in order to get

back to the latest revision and to be able to update with ``git pull``

again, you first will need to first type ``git checkout unstable`` (or

check out any other desired branch).

Once you have updated your local files with a ``git pull`` (or ``git

checkout``), you still need to re-build LAMMPS if any source files have

changed.  To do this, you should cd to the src directory and type:

.. code-block:: bash