changes to Errors and Python doc pages

doc/src/Python_shlib.txt

@@ -0,0 +1,34 @@
+"Higher level section"_Python.html - "LAMMPS WWW Site"_lws - "LAMMPS
+Documentation"_ld - "LAMMPS Commands"_lc :c
+
+:link(lws,http://lammps.sandia.gov)
+:link(ld,Manual.html)
+:link(lc,Section_commands.html#comm)
+
+:line
+
+Build LAMMPS as a shared library :h3
+
+Instructions on how to build LAMMPS as a shared library are given in
+"Section 2.4"_Section_start.html#start_4.  A shared library is one
+that is dynamically loadable, which is what Python requires to wrap
+LAMMPS.  On Linux this is a library file that ends in ".so", not ".a".
+
+From the src directory, type
+
+make foo mode=shlib :pre
+
+where foo is the machine target name, such as mpi or serial.
+This should create the file liblammps_foo.so in the src directory, as
+well as a soft link liblammps.so, which is what the Python wrapper will
+load by default.  Note that if you are building multiple machine
+versions of the shared library, the soft link is always set to the
+most recently built version.
+
+NOTE: If you are building LAMMPS with an MPI or FFT library or other
+auxiliary libraries (used by various packages), then all of these
+extra libraries must also be shared libraries.  If the LAMMPS
+shared-library build fails with an error complaining about this, see
+"Section 2.4"_Section_start.html#start_4 for more details.
+
+Also include CMake info on this