Create vignette for input data requirements

[caitlinch]

Create a vignette for PoolTestR outlining the requirements for input data frames.

It should include:

• Result and PoolSize columns: type (integer/numeric), allowed values (0/1 for Results, >0 for PoolSize)
• Explanation of a hierarchical sampling structure
• Requirements for hierarchical columns (each column in the hierarchical sampling structure should have unique values.)
• Common errors
  • Reusing numbers in columns e.g., restarting counting at 1 within each Village results in many sites with value 1, whereas each site should have a unique value)
  • Missing values in columns (NA/NULL/"")
  • Missing columns
• Other columns (e.g., Year)
• The difference between stratifying the data by variables and the hierarchy input variable

See the PoolTools wiki pages for examples: How to prepare your data for analysis, Hierarchical sampling structure