Add obtaining bindgen docs section

Author: kornilova203

docs/index.md

@@ -1 +1,6 @@
-# Scala Native Bindgen Documentation
+# Scala Native Bindgen
+
+This tool generates Scala Native bindings from C headers.
+It's built upon clang and [LibTooling] and thus respects the conventions of clang-tools.
+
+ [LibTooling]: https://clang.llvm.org/docs/LibTooling.html

docs/obtaining-bindgen.md

@@ -0,0 +1,107 @@
+# Obtaining bindgen
+
+There are 2 ways to obtain bindgen:
+ * [Use docker container](#docker-container) 
+ * [Build binary with CMake](#building-with-cmake)
+ * [Build binary with docker-compose](#building-with-docker-compose)
+
+## Docker container
+
+This option requires [Docker].
+
+Download docker image with the binary:
+
+```sh
+docker pull scalabindgen/scala-native-bindgen
+```
+
+Mount directories with required header files and run bindgen:
+
+```sh
+docker run -v "$(pwd)":/src -v /usr/include:/usr/include \
+  --rm scalabindgen/scala-native-bindgen \
+  relative/path/to/my_header.h --name my_header --
+```
+
+The docker image does not contain standard headers so it is important to
+mount all system include directories that are used by the header file
+passed to `scala-native-bindgen`. See the [docker-bindgen.sh] script for
+how to wrap the dockerized program. The `$CWD` of the container is
+`/src` which should be mounted from `$(pwd)` in case relative paths are
+used.
+
+Note, the `scalabindgen/scala-native-bindgen:latest` image is updated on
+each merge to the `master` branch.
+
+ [Docker]: https://www.docker.com/
+ [docker-bindgen.sh]: scripts/docker-bindgen.sh
+
+## Building with `CMake`
+
+Building `scala-native-bindgen` requires the following tools and libraries:
+
+ - [CMake] version 3.9 or higher
+ - [LLVM] and [Clang] version 5.0 or 6.0.
+
+```sh
+# On apt-based systems
+apt install cmake clang-$LLVM_VERSION libclang-$LLVM_VERSION-dev llvm-$LLVM_VERSION-dev
+
+# With `brew`
+brew install cmake llvm@6
+```
+
+To run the tests you also need the required Scala Native libraries.
+See the [Scala Native setup guide] for instructions on installing the dependencies.
+
+```sh
+mkdir -p bindgen/target
+cd bindgen/target
+cmake ..
+make
+./scala-native-bindgen --name ctype /usr/include/ctype.h --
+```
+
+To build a statically linked executable pass `-DSTATIC_LINKING=ON` when invoking `cmake`:
+
+```sh
+cmake -DSTATIC_LINKING=ON ..
+```
+
+Additional compiler and linker flags may be passed as environment variable sor their CMake
+equivalent, e.g. to compile with debug symbols the following are the same:
+
+```sh
+cmake -DCMAKE_CXX_FLAGS=-g ..
+CXXFLAGS=-g cmake ..
+```
+
+## Building with `docker-compose`
+
+Alternatively, you can use [docker-compose] to build and test the program:
+
+```sh
+# Build the docker image with LLVM version 6.0.
+docker-compose build ubuntu-18.04-llvm-6.0
+# Build the bindgen tool and run the tests.
+docker-compose run --rm ubuntu-18.04-llvm-6.0 ./script/test.sh
+# Run the bindgen tool inside the container.
+docker-compose run --rm ubuntu-18.04-llvm-6.0 \
+    bindgen/target/scala-native-bindgen --name union tests/samples/Union.h --
+```
+
+ [CMake]: https://cmake.org/
+ [LLVM]: https://llvm.org/
+ [Clang]: https://clang.llvm.org/
+ [Scala Native setup guide]: http://www.scala-native.org/en/latest/user/setup.html
+ [docker-compose]: https://docs.docker.com/compose/
+
+## Testing
+
+The tests assume that the above instructions for building `scala-native-bindgen` from source
+has been followed.
+
+```sh
+cd tests
+sbt test
+```