message: document rpath for non-standard install location
diff: @@ -100,6 +100,16 @@ cmake .. \
  -DCMAKE_INSTALL_PREFIX=/usr/local
  ```
  +If installing to a non-standard directory (i.e., one which the dynamic loader does not search),
  +consider specifying the `-DCMAKE_INSTALL_RPATH=` option:
  +
  +```
  +cmake .. \
  + -DCMAKE_BUILD_TYPE=Release \
  + -DCMAKE_INSTALL_PREFIX=/opt/mongo \
  + -DCMAKE_INSTALL_RPATH=/opt/mongo
  +```
  +
  In the Unix examples that follow, `mongocxx` is customized in these ways:
  * `libmongoc` is found in `/opt/mongo-c-driver`.
  