Add a data quality/sourcing/disclaimer page/footer

[nmately]

We should sure our data is clearly sourced with links (if possible) to the sources (not necessarily the full query or raw data unless that's easy; maybe just a link to e.g. NetFile), along with a brief description or disclaimer about the data's coverage and limitations (if any; for example does it include ALL donations, only those over a certain amount, are there any anonymous donations/ways of obscuring the donation source. for example someone mentioned that we can't necessarily assume exact name matches on donors that might be/represent the same people or groups? might be worth including.

This could be a general footer at the bottom of each page, or an "about the data" page that covers the whole tool/site, or if we have data from multiple sources or changing sources for whatever reason maybe a small sourcing line at the bottom of each data table (think how google maps, depending on where you are looking, might have "data from so-and-so-satellite company" or "some imagery courtesy tomtom navigation" or whatever

[jeremiak]

@nmately Thanks for opening the issue! Mind taking a look at #28 to see if it addresses the questions you have or if it's missing anything?

[jeremiak]

This comment from @rileyschenck also should be included on the list of documented things:

One slight quibble would be the wording of "Below is each elected representative and all of the people and organizations who have given them campaign contributions *during their time in local elected office." *

The campaign totals would also include campaign cash raised while still a candidate before being elected to office too, which could potentially be multiple campaigns over multiple years before they took office.