Add note about `--enable-shared` and RPATH (fixes #217)

plugins/python-build/README.md

@@ -105,6 +105,20 @@ process.
   configure and make options for buildling CPython. These variables will
   be passed to Python only, not any dependent packages (e.g. libyaml).
 
+### Building with shared library
+
+You can build CPython with `--enable-shared` to install a version with
+shared object.
+
+If `--enabled-shared` was found in `PYTHON_CONFIGURE_OPTS` or `CONFIGURE_OPTS`,
+`python-build` will automatically set `RPATH` to the pyenv's prefix directory.
+This means you don't have to set `LD_LIBRARY_PATH` or `DYLD_LIBRARY_PATH` for
+the version(s) installed with `--enable-shared`.
+
+```sh
+$ env PYTHON_CONFIGURE_OPTS="--enable-shared` pyenv install 2.7.9
+```
+
 ### Checksum verification
 
 If you have the `shasum`, `openssl`, or `sha256sum` tool installed,