Nowadays there is an easier method than the accepted answer.
All you have to do is create a folder called “jniLibs” under your /src/main directory (ie, /app/src/main/jniLibs) and place your .so files there. It will look like this:
app
|
src
|
main
|
jniLibs
|
armeabi
| |
| your_lib_compiled_for_armeabi.so
|
armeabi-v7a
| |
| your_lib_compiled_for_v7a.so
|
x86
| |
| your_lib_compiled_for_x86.so
Your .so files should be picked up now.