Documentation for the Eval Plugin

[tittoassini]

No description provided.

[jneira]

lgtm, thanks for improving docs!

[jneira]

There was a failing test (but the pr does not change any code so i hope it will be transient, i've reran the build)

-- During interactive linking, GHCi couldn't find the following symbol:\n--   interactive_Ghci1_asPrint_closure\n-- This may be due to you not asking GHCi to load extra object files,\n-- archives or DLLs needed by your current session.  Restart GHCi, specifying\n-- the missing library using the -L/path/to/object/dir and -lmissinglibname\n-- flags, or simply by naming the relevant files on the GHCi command line.\n-- Alternatively, this link failure might indicate a bug in GHCi.\n-- If you suspect the latter, please report this as a GHC bug:\n--   https://www.haskell.org/ghc/reportabug\n\n