Fix the name of the Docker Container image that is used to build the kernel
for an RTVM (Preempt-RT kernel) when that image was built by the user
him/herself.
Tracked-On: #4322
Signed-off-by: Geoffroy Van Cutsem <geoffroy.vancutsem@intel.com>
Move the "Building ACRN in Docker" guide to the "Try using ACRN" section to be
more prominently visible. Reference it from the main "Build ACRN from Source"
user guide.
Signed-off-by: Geoffroy Van Cutsem <geoffroy.vancutsem@intel.com>