Update README with snappy support instructions.

Author: mchav

README.md

@@ -8,6 +8,7 @@ A tool for exploratory data analysis.
 
 ### CLI
 * Install Haskell (ghc + cabal) via [ghcup](https://www.haskell.org/ghcup/install/) selecting all the default options.
+* Install snappy (needed for Parquet support) by running: `sudo apt install libsnappy-dev`.
 * To install dataframe run `cabal update && cabal install dataframe`
 * Open a Haskell repl with dataframe loaded by running `cabal repl --build-depends dataframe`.
 * Follow along any one of the tutorials below.