Update contribution guidelines

[ci skip]
Add options to configure GHC module search [#293]

Add new options to add package databases, disable the user package
database, and add directories to the search path.
Add Verilog checker using Verilator

Support for syntax checking of Verilog code using Verilator, a free Verilog HDL
simulator.  Two test cases are included, one for error messages and another for
warnings.
Merge pull request #296 from dholm/checker/verilog-verilator

Add Verilog checker using Verilator
Improve wording
Update changelog
Merge branch 'haskell-options'

* haskell-options:
  Add options to configure GHC module search [#293]
Bump dependencies