Update README.md on PCL dependency

[AzulRadio]

Hi, thanks for the amazing work on porting FAST_LIO to ROS2!

I'm deploying FAST_LIO on an Nvidia Jetson with Ubuntu 22.04 and ROS 2 Humble and I found some disagreement between the README instructions and what actually happened. So I add my solution to the README.

Changes:

• The PCL default from apt (libpcl-dev) doesn't work for me and FAST_LIO refuses to compile. After I installed pcl_ros the problem was fixed.
• The link for PCL installation no longer directs to a 404 site.

Jetson might not be the hardware people use the most to deploy FAST_LIO so I don't know if the problem is just for ARM arch or everyone. It would be nice if someone could help me verify this.

Thanks again for your work!

[Ericsii]

Much appreciate your contribution. @AzulRadio

This README.md change makes great sense. But I have another question.

• The PCL default from apt (libpcl-dev) doesn't work for me and FAST_LIO refuses to compile. After I installed pcl_ros the problem was fixed.

You said the libpcl-dev from apt is not compatible with Jetson. If so, there should be a change in the package.xml file to fix the dependency problem. Can you provide a detailed build log?

[AzulRadio]

@Ericsii Here you go

Starting >>> fast_lio
--- stderr: fast_lio
Current CPU archtecture: aarch64
CMake Error at CMakeLists.txt:60 (find_package):
  By not providing "Findpcl_ros.cmake" in CMAKE_MODULE_PATH this project has
  asked CMake to find a package configuration file provided by "pcl_ros", but
  CMake did not find one.

  Could not find a package configuration file provided by "pcl_ros" with any
  of the following names:

    pcl_rosConfig.cmake
    pcl_ros-config.cmake

  Add the installation prefix of "pcl_ros" to CMAKE_PREFIX_PATH or set
  "pcl_ros_DIR" to a directory containing one of the above files.  If
  "pcl_ros" provides a separate development package or SDK, be sure it has
  been installed.

---
Failed   <<< fast_lio [2.16s, exited with code 1]

Summary: 0 packages finished [3.87s]
  1 package failed: fast_lio
  1 package had stderr output: fast_lio

[Ericsii]

It seems you didn't use rosdep install --from-paths src --ignore-src -y this command to install dependencies. Can you help me add this line to README.md?

[Ericsii]

LGTM