add compilation readme

Author: arik-so

README.md

@@ -0,0 +1,105 @@
+# ldk-swift
+
+Automatic Swift bindings generation for [`rust-lightning`](https://github.com/lightningdevkit/rust-lightning).
+
+## Installation
+
+In order to use the automatically generated bindings, simply drag `*.xcframework` file into an Xcode project.
+
+The `*.xcframework` files are either available on 
+the [Releases](https://github.com/lightningdevkit/ldk-swift/releases) page, or can be [compiled](#Compilation)
+from scratch.
+
+
+## Compilation
+
+### Cloning Dependencies
+
+In order to generate these bindings from scratch, you will need to clone two dependency repositories:
+
+**rust-lightning**, (a specific branch built for bindings compatibility) 
+```shell
+git clone --branch 2021-03-java-bindings-base [email protected]:TheBlueMatt/rust-lightning.git
+```
+
+**ldk-c-bindings**
+```shell
+git clone [email protected]:lightningdevkit/ldk-c-bindings.git
+```
+
+### Generating Rust-to-C-bindings
+
+Now, navigate to the `ldk-c-bindings` directory and run the `genbindings.sh` script:
+
+```shell
+cd /path/to/ldk-c-bindings
+./genbindings.sh /path/to/rust-lightning true
+```
+
+### Generating C-to-Swift-bindings
+
+<details>
+<summary>If using Docker</summary>
+
+If you're using Docker to generate the Swift bindings, navigate (if you're not already there from the 
+previous step) to the `ldk-c-bindings` directory and open the file located here:
+
+`/path/to/ldk-c-bindings/lightning-c-bindings/Cargo.toml`
+
+In that file, you will see four lines specifying the `lightning`, `lightning-persister`, `lightning-invoice`, and 
+`lightning-background-processor` dependencies. They will most likely show local paths to the `rust-lightning` 
+folder due to the previous `genbindings.sh` step. As Docker won't have access to local paths,
+replace those lines with the following:
+
+```yaml
+lightning = { git = "https://github.com/thebluematt/rust-lightning", rev = "xxx", features = ["std"] }
+lightning-persister = { git = "https://github.com/thebluematt/rust-lightning", rev = "xxx" }
+lightning-invoice = { git = "https://github.com/thebluematt/rust-lightning", rev = "xxx" }
+lightning-background-processor = { git = "https://github.com/thebluematt/rust-lightning", rev = "xxx" }
+```
+
+You will note that the revision is unspecified and is currently just placeholder `xxx`s. To obtain the revision, 
+just navigate to the just clone custom `rust-lightning` directory and run:
+
+```shell
+cd /path/to/rust-lightning
+git rev-parse HEAD
+```
+
+Take that commit hash and replace the `xxx` instances with it. 
+</details>
+
+#### Generating the Swift files
+
+To generate the Swift files, navigate to the `ldk-swift` repository and run the following:
+
+```shell
+EXPORT LDK_SWIFT_GENERATOR_INPUT_HEADER_PATH="/path/to/ldk-c-bindings/lightning-c-bindings/include/lightning.h"
+python3 ./
+```
+
+Now, the contents of the `bindings/LDK` folder will have been completely regenerated.
+
+#### Generating the *.xcframework files
+
+With the Swift files completely regenerated, you will need to make sure the Xcode projects that serve as bases
+for the `*.xcframework`s reference them correctly. So navigate here:
+
+`path/to/ldk-swift/xcode`
+
+and open the respective `*.xcodeproj` files located in the `LDKFramework` and `LDKFramework_Mac` directories. 
+Do the following steps for _both_ projects:
+
+1. Remove the `LDK` references in the Xcode file tree
+2. Drag the `path/to/ldk-swift/bindings/LDK` folder to that same location in the file tree
+3. Check `Copy items if needed` and pick `Create groups` in the dialog box
+
+Next, navigate back to the `xcode` directory, and run the following scripts:
+
+```shell
+./compile_dependency_binaries.sh /path/to/ldk-c-bindings
+./build_framework.sh 
+```
+
+Finally, navigate to `path/to/ldk-swift/bindings/bin`, and you should find multiple `*.xcframework` files
+waiting for you there.