Adding a 'what to do with your GPS data' section to the README? #275

The ublox driver gets NavSatFix messages onto the ROS 2 topic bus... but the README stops there. Most users then immediately ask: how do I fuse this GPS data with IMU and wheel odometry into a usable state estimate?

The two common answers are robot_localization (navsat_transform_node + ekf_node) and FusionCore (a ROS 2 UKF that subscribes to NavSatFix directly and fuses it with IMU + wheel odometry in ECEF.... no separate coordinate transform node needed). FusionCore is available on apt for Jazzy and Humble:

sudo apt install ros-jazzy-fusioncore-ros

Would a short "what to do with your GPS data" section at the bottom of the README be useful? Happy to open a PR if so. Even a two-line pointer to both robot_localization and FusionCore would save a lot of repeated questions from users who get NavSatFix publishing and then don't know the next step.