Added readme file.

README.md

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+# MODFLOW EXECUTABLES
+
+The purpose of this repository is to distribute binary executable programs for MODFLOW and related programs that will run on Windows, Mac, and Linux operating systems. Executables for these different operating systems can be found under the release tab and will be named win64.zip, win32.zip, mac.zip, and linux.zip.
+
+The programs and version numbers for the present release are
+
+| Program | Version |
+|--- |---|
+| MODFLOW 6 | 6.0.3 |
+| MODFLOW-2005 | 1.12 |
+| MODFLOW-NWT | 1.1.4 |
+| MODFLOW-USG | 1.3 |
+| MODPATH-6 | 6.0.1 |
+| MODPATH-7 | 7.2.1 |
+| MT3DMS | 5.3.0 |
+| MT3D-USGS | 1.0.0 |
+| SEAWAT | 4.0.5 |
+| MODFLOW-2000 | 1.19 |
+| MODFLOW-LGR | 2.0 |
+
+These programs are compiled using [pymake](https://github.com/modflowpy/pymake) and the Intel compiler.
+