add some external links

Author: wkliao

README.md

@@ -9,11 +9,12 @@ classic formats. The software development is a collaborative work of
 Northwestern University and Argonne National Laboratory.
 
 * The original repository: https://svn.mcs.anl.gov/repos/parallel-netcdf
-* Since June 1, 2018, PnetCDF repository has been migrated to
-  here, https://github.com/Parallel-NetCDF/PnetCDF, on github.com.
+* Since June 1, 2018, the PnetCDF repository has been migrated to
+  here on github.
 
-### PnetCDF project web page
+### PnetCDF project home page
 * https://parallel-netcdf.github.io
+  contains more information about PnetCDF.
 
 ### PnetCDF official software releases
 * All **official released versions** can be found in
@@ -27,36 +28,38 @@ Northwestern University and Argonne National Laboratory.
 ### Build PnetCDF using source codes of this development repository
 * The source codes in this repository are constantly under development. They
   should **NOT** be used for production runs.
-* Use the source codes in this repository only if you are interested in
-  contributing the project and we welcome and appreciate any contribution.
-* To clone this repository, run command
+* Building PnetCDF using the source codes in this repository only if you are
+  interested in contributing the project and we welcome and appreciate any
+  contribution.
+* Required software
+  + MPI compilers, e.g. [MPICH](https://www.mpich.org) and
+    [OpenMPI](https://www.open-mpi.org)
+  + [autoconfig](https://www.gnu.org/software/autoconf) version 2.70
+  + [automake](https://www.gnu.org/software/automake) version 1.16.5
+  + [libtool](https://www.gnu.org/software/libtool) version 2.4.6
+  + [m4](https://www.gnu.org/software/m4) version 1.4.17
+* Clone, build, and installation commands:
   ```console
   git clone https://github.com/Parallel-NetCDF/PnetCDF.git
-  ```
-  This will create a new folder named `PnetCDF`.
-* Before running configure command to build PnetCDF, please run commands below
-  first.
-  ```console
+
   cd PnetCDF
   autoreconf -i
+
+  ./configure --prefix=/install/path --with-mpi=/mpi/path
+  make install
   ```
-  Several files, e.g. configure and Makefile.in, will be created for running the
-  configure command. The minimum versions of GNU autotools required are:
-  + [autoconfig](https://www.gnu.org/software/autoconf/autoconf.html) version 2.70
-  + [automake](https://www.gnu.org/software/automake) version 1.16.5
-  + [libtool](https://www.gnu.org/software/libtool) version 2.4.6
-  + [m4](https://www.gnu.org/software/m4/m4.html) version 1.4.17
 
 ### Build instructions and recipes
 * Please read file [INSTALL](./INSTALL) for build instructions. There are also
   several build recipes under folder [doc](./doc#readme) for a few popular
   systems.
 
-### PnetCDF user guides
+### Users documents
 * [C API references](https://parallel-netcdf.github.io/doc/c-reference/pnetcdf-c/index.html)
 * [Questions & Answers](https://parallel-netcdf.github.io/doc/faq.html)
+* [Utility Programs](./src/utils#readme)
 * [NetCDF4 vs. PnetCDF](./doc/netcdf4_vs_pnetcdf.md)
-* [PnetCDF blocking vs. non-blocking APIs](./doc/blocking_vs_nonblocking.md)
+* PnetCDF [blocking vs. non-blocking APIs](./doc/blocking_vs_nonblocking.md)
 
 ### Mailing List
 * [email protected]
@@ -65,6 +68,16 @@ Northwestern University and Argonne National Laboratory.
   + The past discussions in the mailing list are available in:
     http://lists.mcs.anl.gov/pipermail/parallel-netcdf/.
 
+### External links to some related projects and application users
+* [PnetCDF Python](https://github.com/Parallel-NetCDF/PnetCDF-Python),
+  a python interface to PnetCDF library.
+* [E3SM I/O kernel study](https://github.com/Parallel-NetCDF/E3SM-IO)
+* [Scorpio](https://github.com/E3SM-Project/scorpio), the I/O module of E3SM.
+* [PIO](https://github.com/NCAR/ParallelIO) - parallel I/O library at NCAR.
+* [WRF](https://github.com/wrf-model/WRF/tree/master/external/io_pnetcdf)
+  - Weather Research & Forecasting Model at NCAR.
+
+
 ### Acknowledgements
 * Ongoing development and maintenance of PnetCDF-python is supported by the
   U.S. Department of Energy's Office of Science, Scientific Discovery through