README files for Android SDK and mentat_ffi

ffi/README.md

@@ -0,0 +1,22 @@
+# Development flow for Mentat FFI
+
+## Android SDK
+Android Mentat SDK is one of two first-party consumers (the other one being iOS Mentat SDK).
+
+Binaries produced by `cargo build ...` are symlinked from within the SDK, and a number of target-specific `libmentat_ffi.so` binaries are bundled together and distributed with the SDK.
+
+There is a build script at `<mentat_root>/scripts/android_build.sh` which knows how to cross-compile `mentat_ffi` for various Android targets.
+
+- `./<mentat_root>/scripts/android_build.sh` - compiles for all supported targets
+- `./<mentat_root>/scripts/android_build.sh x86` - compiles for `x86`
+- `./<mentat_root>/scripts/android_build.sh x86 arm` - compiles for `x86`, `arm` 
+
+General development flow while working on the Android SDK is:
+- (pre) compile for all targets, if you've never done so
+- make changes to `mentat_ffi` and/or `mentat`
+- re-compile `mentat_ffi` binaries using `./android_build.sh x86`. During development it's faster to compile just for the target which matches your emulator, e.g. `x86`
+- make corresponding changes in the Android SDK, try them out from within the bundled sample project
+- since binaries are symlinked, no manual copy step is necessary for the Android SDK to pick up the changes
+
+## iOS SDK
+TODO, contribute via [issue #732](https://github.com/mozilla/mentat/issues/732).

sdks/android/README.md

@@ -0,0 +1,8 @@
+# Android Mentat SDK
+
+Exposes Mentat functionality to Android applications via the foreign function interface provided by `mentat_ffi`.
+
+Note that `libmentat_ffi.so` binaries are symlinked. Use [the cross-compilation script](https://github.com/mozilla/mentat/tree/master/scripts/android_build.sh) to build them. Windows users: apologies if you're on FAT; symlinks are supported on NTFS (on Vista and later).
+
+- See [sample projects](https://github.com/mozilla/mentat/tree/master/sdks/android/Mentat/samples) for how one might use the SDK.
+- See [documentation](https://github.com/mozilla/mentat/tree/master/ffi/README.md) within the `mentat_ffi` crate for development flow.