Update README.md

README.md

 # UVic-updates-opem: Optimality-based Plankton Ecosystem Model (OPEM) for the UVic-ESCM
 
+Markus Pahlow (mpahlow@geomar.de)
+
 UVic-updates-opem introduces optimality-based phytoplankton and zooplankton into the UVic-ESCM (version 2.9) with variable C:N:P(:Chl) stoichiometry for phytoplankton, diazotrophs, and detritus.  Code development started with and has incorporated updates provided by David Keller, Karin Kvale, and Levin Nickelsen.
 
 ## Setup
@@ -17,3 +19,7 @@ HNO<sub>3</sub> + 1.5 H<sub>2</sub>O -> NH<sub>3</sub> + 0.5 H<sub>2</sub>O + 2
 * Fixed bug sometimes inflating negative concentrations: do not limit `tnpzd` to positive values in subroutine `tracer`, as this interferes with the flag mechanism in `npzd_src`.
 * If `timavgint=30`, i.e., not a divisor of a year (365 days), the first month will be skipped if starting at the beginning of the year and the year is not a multiple of 30.  -> set `init_time_in = .true.` in namelist `ictime`.
 * Positive particulate tracers can be enforced by activating `O_fct_3d` and `O_opem_pos` in mk.in.
+
+## License
+
+This work is published under the [GNU General Public License 3 (GPL-3.0)](http://opensource.org/licenses/GPL-3.0).  You may copy, distribute and modify the software as long as you track changes/dates of in source files and keep modifications under GPL. You can distribute your application using a GPL library commercially, but you must also provide the source code."