Documentation (#110)

Expands readme with basic build instructions, needs more details

Co-authored-by: Sam Reeve <[email protected]>

README.md

@@ -1 +1,91 @@
-Picasso
+# Picasso
+
+Picasso is a performance portable library for particle-in-cell (PIC) simulations
+which are used in applications including plasmas physics and fluid/solid
+mechanics. Picasso provides a range of interpolation schemes between
+particles and grids, both in order of the scheme and the type
+(FLIP, APIC, PolyPIC), embedded free-surface tracking, extensive batched 
+linear algebra capabilties, as well as utilities for managing field data
+and simplifying parallel execution.
+
+## Dependencies
+
+Picasso's main dependency is [Cabana](https://github.com/ECP-copa/Cabana).
+The instructions for building Cabana can be found in the [Cabana wiki](https://github.com/ECP-copa/Cabana/wiki/1-Build-Instructions)
+Cabana requires the Kokkos library and must be built with the optional Cabana::Grid
+subpackage enabled (which in turn requires MPI).
+
+Picasso Dependencies
+| Dependency |Required | CMake Variable | Details |
+| ---------- | ------- | -------------  | ------  |
+|[CMake](https://cmake.org/download/)      | Yes     | Build system |
+|[Kokkos](https://github.com/kokkos/kokkos)    | Yes      | Portable on-node parallelism |
+|[Cabana](https://github.com/ECP-copa/Cabana) | Yes | Performance-portable particle and grid library |
+|MPI | Yes | Message Passing Interface |
+|[JSON](https://github.com/nlohmann/json) | Yes | JSON input files |
+|ArborX | No | Picasso_REQUIRE_ARBORX | Performance-portable geometric search (required for level-set) | N/A |
+|GTest | No | Picasso_REQUIRE_TESTING |Unit test Framework | N/A |
+
+In addition to these required dependencies, note that Cabana must be built with
+`Cabana_ENABLE_GRID=ON` (enabled by default) and will need further options as noted below for some additional capabilities.
+
+There are additional optional dependencies for Picasso that depend on the 
+use case desired or hardware type on the system.
+
+Picasso dependencies imported from Cabana. Note that the `REQUIRE` variables enforce that those options are
+available for Cabana at configuration, but are not necessary.
+| Dependency |Required | CMake Variable | Details |
+| ----------| -------- | -------------- | -------  |
+| HDF5 | No | Cabana_REQUIRE_HDF5 | Particle I/O |
+| Silo | No | Cabana_REQUIRE_SILO | Particle I/O |
+| CUDA | No | Cabana_REQUIRE_CUDA | Programming model for NVIDIA GPUs |
+| HIP  | No | Cabana_REQUIRE_HIP  | Programming model for AMD GPUs |
+| SYCL | No | Cabana_REQUIRE_SYCL | Programming model for Intel GPUs |
+
+## Building Picasso
+
+To build Picasso, clone the repository via
+`git clone https://github.com/picassodev/picasso.git`. Ensure that
+you have an install of Cabana with the grid build option
+enabled ([Cabana Build Details](https://github.com/ECP-copa/Cabana/wiki/1-Build-Instructions)
+
+A [Cabana Docker container](https://github.com/ECP-copa/Cabana/pkgs/container/cabana)
+is maintained to facilitate development with most optional dependencies.
+
+From the the source directory, run the following script to create
+a build directory for Picasso, configure the Picasso build in that
+directory, and build Picasso in that directory
+
+```
+# Change directory as needed
+export CABANA_DIR='pwd'/Cabana/build/install
+
+cd picasso
+cmake \
+  -B build
+  -D CMAKE_BUILD_TYPE=Release \
+  -D CMAKE_PREFIX_PATH="$CABANA_DIR" \
+  -D CMAKE_INSTALL_PREFIX=install \
+  -D Picasso_ENABLE_TESTING=ON
+cmake --build build
+cmake --install build
+```
+
+## Testing Picasso
+
+To test your Picasso install, from the build directory of a Picasso
+build run with testing enabled, run the `ctest` command and ensure
+that all tests list as passing
+
+## Contributing
+
+We encourage you to contribute to Picasso! Please check the
+[guidelines](CONTRIBUTING.md) on how to do so.
+
+## Citing
+
+If you use Picasso in your work, please cite the appropriate [release](https://doi.org/10.5281/zenodo.8309476).
+
+## License
+
+Picasso is distributed under an [open source 3-clause BSD license](LICENSE).