added license file

DEVELOPERS

+
+This list shows people who have repository access to GADGET-4, and
+contribute actively to its development.
+
+Name                 Email                                      Institution
+
+Volker Springel      vspringel@mpa-garching.mpg.de              MPA
+Ruediger Pakmor	     rpakmor@mpa-garching.mpg.de                MPA
+Oliver Zier	     ozier@mpa-garching.mpg.de                  MPA
+Martin Reinecke      martin@mpa-garching.mpg.de                 MPA

README.md

@@ -3,54 +3,32 @@
 GADGET-4
 ========
 
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+  ___    __    ____    ___  ____  ____       __
+ / __)  /__\  (  _ \  / __)( ___)(_  _)___  /. |
+( (_-. /(__)\  )(_) )( (_-. )__)   )( (___)(_  _)
+ \___/(__)(__)(____/  \___/(____) (__)       (_)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+GADGET-4 is a massively parallel code for N-body/hydrodynamical
+cosmological simulations. It is a flexible code that can be applied to
+a variety of different types of simulations, offering a number of
+sophisticated simulation algorithms.  An account of the numerical
+algorithms employed by the code is given in the original code paper,
+subsequent publications, and this documentation.
+
+GADGET-4 was written mainly by
+[Volker Springel](mailto:vspringel@mpa-garching.mpg.de), with
+important contributions and suggestions being made by numerous people,
+including [Ruediger Pakmor](mailto:rpakmor@mpa-garching.mpg.de),
+[Oliver Zier](mailto:ozier@mpa-garching.mpg.de), and
+[Martin Reinecke](mailto:martin@mpa-garching.mpg.de).
+
 
 Documentation
 =============
 
-To build a local copy of the documentation:
-
-- run `doxygen`
-
-- open `doxygen/html/index.html` in a browser
-
-
-Developers
-==========
-
-See the file DEVELOPERS.
-
-
-LIMITS
-======
-
-
-* Maximum number of particles per MPI-rank is restricted to 2^31 ~ 2 Billion
-
-* Maximum number of groups/subhalos per MPI-rank is restricted to 2^31 ~ 2 Billion
-
-* The total number of particles, and the total number of groups/subhalos, can however
-  be much larger than this if a sufficiently large number of MPI ranks is used. 
-  
-* Maximum particle number in a single group or subhalo is for the default setting  2^31 ~ 2 billion, 
-  but this can be enlarged if needed by setting the option FOF_ALLOW_HUGE_GROUPLENGTH
-  
-* The maximum number of subhalos per group is restricted nevertheless to 2^31 ~ 2 billion.
-  
-* If the legacy output formats 1/2 are used, each block in the output is restricted to 2 Gbyte in 
-  size or less. This also means that the maximum number of particles per single output file, and the
-  maximum number of groups/subhalos per single group catalogue file can be at most of order 2 Billion,
-  normally substantially less than that. While this restriction can be circumvented by splitting output
-  over enough files, it provides one further motivation to use the HDF5 formay!
-  
-* Maximum number of lightcones: 256
-
-* If more MPI-ranks than PMGRID are used, not all MPI tasks get anything to do in FFT calculations, which severely 
-  compromises achievable work-load and memory balance. In this case, the column-based FFT algorithm is
-  a way out (it incurs higher cost however, as twice as many transpose operations are needed)
-
-
-
-
-
+For documentation of the code as well as the code paper, please refer
+to the [code's web-site](https://wwwmpa.mpa-garching.mpg.de/gadget4).