Extend RAJA launch docs

[artv3]

Further describe capabilities such as cuda_global_thread_{x,y,z}, tiling, omp parallel regions.

Missing docs reported in https://github.com/LLNL/RAJA/issues/1057

• [x] Basic overview of API
• [x] Run-time CPU/GPU switching
• [x] Overview of hierarchical parallelism using teams and threads
• [x] Usage of kernel naming using NVTX and ROCTX
• [x] Static shared memory usage
• [x] Dynamic shared memory usage
• [x] launch types, seq_launch_t, omp_launch_t, cuda_launch_t
• [ ] loop tiling

[artv3]

@artv3 - make a list of what is covered vs not covered

[rhornung67]

@artv3 I think the items for the unchecked boxes above are now covered. Please verify and close or update this issue, whichever applies.