unified and better log/error messages for CDBEnv/CDB
Add gitian build guide

Work in progress...
Merge pull request #3994

2c47a00 Add gitian build guide (Wladimir J. van der Laan)
Merge pull request #3572

f7257cf unified and better log/error messages for CDBEnv/CDB (Philip Kaufmann)
Update README.md
Merge pull request #4005 from Telepatheic/patch-1

Update README.md