Tutorial issues

[smpark7]

Moltres needs more tutorials with better descriptions. This issue can be closed when:

• [ ] the main README references the tutorial directory to lead users there
• [ ] the READMEs of the existing tutorials are improved for clarity
• [x] the three existing tutorials for group constant generation are consolidated
• [x] a new tutorial directory is created to accommodate this example instead of the current link to a test input file
• [ ] new tutorials are created for
  • [x] Eigenvalue calculation
  • [ ] Precursor looping
  • [ ] Navier-Stokes flow coupling