Update readme

README.md

-# csg-eb
+# CSG-EB
 
-Library for parsing [Constructive Solid Geometry (CSG)
-files](https://github.com/openscad/openscad/wiki/CSG-File-Format) into an
-implicit function that can be used to define [Embedded Boundaries
+This library is for parsing [Constructive Solid Geometry
+(CSG)](https://github.com/openscad/openscad/wiki/CSG-File-Format) for use in
+[AMReX Embedded Boundaries
 (EB)](https://amrex-codes.github.io/amrex/docs_html/EB.html).
 
-Uses PEGTL for parsing and Catch2 for tests.
+CSG is a file format used by the open source CAD modelling tool
+[OpenSCAD](https://www.openscad.org). CSG is a subset of the SCAD language,
+equivalent in the kinds of geometries that can be expressed, but with fewer
+primitives (OpenSCAD can export `.scad` files to `.csg`). SCAD code is easier to
+read and write by humans; CSG files are easier to parse and process by software.
 
+Dependencies:
 
-## Build
+ - [PEGTL](https://github.com/taocpp/PEGTL) for parsing
+ - [Catch2](https://github.com/catchorg/Catch2) for testing framework
+ - [CGAL](https://www.cgal.org) for geometry computation
 
-> :warning: **Requires C++17, such as GCC 7.x or later, or Clang 5.x or later**.
 
-### CMake
 
-#### Installing conan for the first time
+## How to Build
 
-    python3 -m pip install conan
+### Build dependencies
 
-#### Building using CMake
+ - C++17 compiler (GCC >=7.x, Clang >=5.x)
+ - CMake >=3.14
+ - Conan (CMake will try to install Conan if `conan` is not in `PATH`)
 
-    cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
-    cmake --build build --target unit_tests_csg
-    cd build
-    make -j
+CMake will try to install [Conan](https://conan.io) if `conan` is not in `PATH`.
+However, installing Conan (`pip install conan`) is recommended for faster builds.
 
-#### Running unit tests
+#### Build
 
-    ctest
+```shell
+> cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
+> cmake --build build
+```
 
+#### Run tests
 
-## Using the library in other projects
+```shell
+> cd build
+> ctest
+```
 
-### Include in the code
-* Include the header file
 
-        #include "csg.hpp"
+## Using CSG-EB in your project
 
-* Create a function object
+ - Include the header file `csg.hpp`
+ - Call `csg::get_csgif` with the path to a CSG file to create an [Implicit Function object](https://amrex-codes.github.io/amrex/docs_html/EB.html#implicit-function).
 
-        auto csg_if = csg::get_csgif(<path_to_file_with_csg_extension>, is_internal_flow);
+```cpp
+#include <csg.hpp>
 
-* Above returns an implicit function which can be operated on a 3D point coordinate (x, y, z) as
+// for EB2::makeShop
+#include <AMReX_EB2_GeometryShop.H>
 
-        csg_if(x, y, z)
+...
 
-* Can be passed to amrex EB2::makeShop
 
-        auto gshop = EB2::makeShop(*csg_if);
+auto csg_file = "~/my_geometry.csg";
+auto is_internal_flow = true;
+
+auto csg_if = csg::get_csgif(csg_file, is_internal_flow);
+
+auto gshop = EB2::makeShop(*csg_if);
+
+```
 
 
 ### Note on the return value
-* If `internal_flow` is set to `true`
-    - **csg_if(x, y, z)** returns a number `less than 0`, if (x, y, z) lies `inside` the CSG object (a hollow)
-    - **csg_if(x, y, z)** returns a number `greater than 0`, if (x, y, z) lies `outside` the CSG object (a hollow)
-* If `internal_flow` is set to `false`
-    - **csg_if(x, y, z)** returns a number `greater than 0`, if (x, y, z) lies `inside` the CSG object (a solid)
-    - **csg_if(x, y, z)** returns a number `less than 0`, if (x, y, z) lies `outside` the CSG object (a solid)
+
+If `is_internal_flow==true`, the CSG geometry defines a hollow space for the domain:
+
+   - csg_if(x, y, z) < 0 ⇒ (x, y, z) is **INSIDE**
+   - csg_if(x, y, z) > 0 ⇒ (x, y, z) is **OUTSIDE**
+
+If `is_internal_flow==false`, the CSG geometry defines a solid boundary to the domain:
+
+   - csg_if(x, y, z) < 0 ⇒ (x, y, z) is **OUTSIDE**
+   - csg_if(x, y, z) > 0 ⇒ (x, y, z) is **INSIDE**
+
 
 ### Add to the CMake build
-* Add this repo as a git submodule
-* Build by adding as subdirectory in appropriate CMake file
 
-        add_subdirectory(<path-to-submodule>)
+* Add this repo as a CMake subdirectory in your `CMakeLists.txt`:
+
+```cmake
+add_subdirectory(/path/to/repo/csg-eb)
+```
 
-* Link by setting the dependency in appropriate CMake file
+* Add the `csg` target to the CMake target that uses code like in the the above example:
 
-        target_link_libraries(<target> PRIVATE csg)
+```cmake
+target_link_libraries(<target> PRIVATE csg)
+```