Update README

README.rst

@@ -18,6 +18,59 @@ be coordinated through CSEG at NCAR.
 
 .. contents::
 
+Software requirements
+=====================
+
+Software requirements for installing, building and running CESM
+---------------------------------------------------------------
+
+Installing, building and running CESM requires:
+
+* a Unix-like operating system (Linux, AIX, OS X, etc.)
+
+* git client version 1.8 or newer
+
+* subversion client (we have tested with versions 1.6.11 and newer)
+
+* python2 version 2.7 or newer (cime supports python3, but some CESM components are not python3-compliant)
+
+* perl version 5
+
+* build tools gmake and cmake
+
+* Fortran and C compilers
+
+  * See `Details on Fortran compiler versions`_ below for more information 
+
+* LAPACK and BLAS libraries
+
+* a NetCDF library version 4.3 or newer built with the same compiler you
+  will use for CESM
+
+  * a PnetCDF library is optional
+
+* a functioning MPI environment (unless you plan to run on a single core
+  with the CIME mpi-serial library)
+
+Details on Fortran compiler versions
+------------------------------------
+The Fortran compiler must support Fortran 2003 features. However, even
+among mainstream Fortran compilers that claim to support Fortran 2003,
+we have found numerous bugs. Thus, many compiler versions do *not* build
+or run CESM properly (see
+https://wiki.ucar.edu/display/ccsm/Fortran+Compiler+Bug+List for more
+details on older Fortran compiler versions).
+
+CESM2 is tested on several different systems with newer Fortran compilers:
+Please see `CESM2.0 Compiler/Machine Tests <https://docs.google.com/spreadsheets/d/15QUqsXD1Z0K_rYNTlykBvjTRt8s0XcQw0cfAj9DZbj0/edit#gid=0>`_
+for a spreadsheet of the current results.
+
+More details on porting CESM
+----------------------------
+
+For more details on porting CESM to a new machine, see
+http://esmci.github.io/cime/users_guide/porting-cime.html
+
 Obtaining the full model code and associated scripting infrastructure
 =====================================================================