Merge #8965: Mention that PPA doesn't support Debian

b55d823 Explicitly state that PPA is for Ubuntu only (anduck)

doc/build-unix.md

@@ -79,7 +79,9 @@ install necessary parts of boost:
 
         sudo apt-get install libboost-all-dev
 
-BerkeleyDB is required for the wallet. db4.8 packages are available [here](https://launchpad.net/~bitcoin/+archive/bitcoin).
+BerkeleyDB is required for the wallet.
+
+**For Ubuntu only:** db4.8 packages are available [here](https://launchpad.net/~bitcoin/+archive/bitcoin).
 You can add the repository and install using the following commands:
 
     sudo apt-get install software-properties-common