Add Markdown README.md with installation info

Author: Damian Rouson

README.md

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+Overview
+========
+This repository exists as a staging ground for developing candidate
+contributions to the GNU Compiler Collection ([GCC]).
+
+Candidate features currently on this site are listed below.  The checked items indicate features 
+that are deemed sufficiently functional submitted to the relevant GCC developer mailing list for review.
+We welcome user feedback from testing these features.  Unchecked itmes are insufficiently mature to 
+submit to GCC.  We welcome code via [pull request] for any listed features or other unsupported
+features of the draft Fortran 2015 standard:
+
+- [X] The [teams branch] with experimental support for Fortran 2015 teams. 
+- [X] The [download-opencoarrays-mpich branch] modifying GCC's prequisites download script
+  to add [OpenCoarrays] and [MPICH] to the list of downloade software.
+- [ ] The [issue-#6-iso-fortran-binding-h branch] providing gthe Fortran 2015 `iso_fortran_binding.h` file.
+
+Installation
+============
+This fork's [releases] are produced from the [teams branch], which expect will be of 
+most interest to users.   We recommend building releses usin the [OpenCoarrays] 
+installation script as follows:
+```bash
+git clone https://github.com/sourceryinstitute/opencoarrays
+cd oppencoarrays
+./install.sh --package gcc \
+  --from-url https://github.com/sourceryinstitute/gcc/archive/<release-tag>.tar.gz \
+  --install-version teams-20170921
+```
+where <version-number> and <release-tag> must be replaced with the appropriate strings such as
+1.9.2 and teams-20170921, respectively.  The final command above peforms the safest but slowest
+build, which could take several hours to complete.  For a speedier build, add the `--disable-bootstrap`,
+which might fail if the GCC you are using to build is too old.  Also, for an interactive build,
+add `--yes-to-all` to instruct the installer to assume affirmative answers to any queries. If successful,
+the above steps will install GCC in the prerequisites/installations subdirectory.  To see additional
+installation options, including choosing another installation path, execute `./install.sh --help`.
+
+For access to any Fortran 2015 parallel features, including teams and failed images, build the [MPICH] 
+and the [opencoarrays-teams branch]:
+of OpenCoarrays:
+```bash
+git checkout opencoarrays-teams
+export LD_LIBRARY_PATH=<gcc-fork-install-path>/lib64:$LD_LIBRARY_PATH
+./install.sh  --package mpich \
+   --with-fortran <gcc-fork-install-path>/bin/gfortarn \
+   --with-c       <gcc-fork-install-path>/bin/gcc      \
+   --with-cpp     <gcc-fork-install-path>/bin/g++
+./install.sh  \
+   --with-mpi <mpich-install-path> 
+```
+with appropriate substitutions for the values between angular brackdets (<...>).  Please report
+any problems with the above steps on our [issues page].
+
+
+[GCC mirror] README
+===================
+
+This directory contains the GNU Compiler Collection (GCC).
+
+The GNU Compiler Collection is free software.  See the files whose
+names start with COPYING for copying permission.  The manuals, and
+some of the runtime libraries, are under different terms; see the
+individual source files for details.
+
+The directory INSTALL contains copies of the installation information
+as HTML and plain text.  The source of this information is
+gcc/doc/install.texi.  The installation information includes details
+of what is included in the GCC sources and what files GCC installs.
+
+See the file gcc/doc/gcc.texi (together with other files that it
+includes) for usage and porting information.  An online readable
+version of the manual is in the files gcc/doc/gcc.info*.
+
+See http://gcc.gnu.org/bugs/ for how to report bugs usefully.
+
+Copyright years on GCC source files may be listed using range
+notation, e.g., 1987-2012, indicating that every year in the range,
+inclusive, is a copyrightable year that could otherwise be listed
+individually.
+
+[GCC mirror]: https://github.com/gcc-mirror/gcc
+[GCC]: https://gcc.gnu.org/gcc
+[OpenCoarrays]: https://www.opendcoarrays.org
+[MPICH]: https://www.mpich.org
+[teams branch]: https://github.com/sourceryinstitute/gcc/tree/teams
+[issue-#6-iso-fortran-binding-h branch]: https://github.com/sourceryinstitute/gcc/tree/issue-#6-iso-fortran-binding-h
+[download-opencoarrays-mpich branch]: https://github.com/sourceryinstitute/gcc/tree/download-opencoarrays-mpich 
+[releases] https://github.com/sourceryinstitute/gcc/releases/
+[issues page] https://github.com/sourceryinstitute/gcc/issues/
+[opencoarrays-teams branch]: https://github.com/sourceryinstitute/opencoarrays/tree/opencoarrays-teams