[savanthongvanh]

Summary

• Add a GEO regional capital-cost difference for all counties in the default input table, covering ReEDS geothermal technologies in the GEO subset.
• Use the state mean of reported geothermal location variations in EIA Table 1-11, subtracting 1.0; use a neutral difference where EIA reports N/A.
• Document the source and statewide averaging approach.

Fixes #233

[bsergi]

Our interpretation of the data in Table 1-11 is slightly different; instead of state-wide averages we map from the cities provided to the nearest county. PR #255 takes a pass at implementing this approach if you'd like to use it for your work.

Given the other PR with a fix I think we can close this one, but thanks for taking a pass at it!