MariaDB-Galera requires some minimal configuration to start a node. When we install it over an existing MariaDB/MySQL cnf file, conflicts between the required and existing configuration are understandable. However, if we install our own cnf files (e.g. upon a new clean installation), it would be nice to provide them with the required options or at least with suggestions (in comments).

1. bind-address in deb packages: do NOT set it in MariaDB-Galera cnf files since it won't work anyway;

2. According to Codership wiki page, the following options are required:
wsrep_provider # as said before, it could be added as a comment
wsrep_cluster_address # also could be added as a comment, with an example of a value
binlog_format=ROW # can be set in cnf
default_storage_engine=InnoDB # can be set in cnf (not necessarily, since it's InnoDB anyway)
innodb_autoinc_lock_mode=2 # can be set in cnf
innodb_locks_unsafe_for_binlog=1 # can be set in cnf

And the following is optional:

innodb_flush_log_at_trx_commit=2 - it could be added as a comment

3. If we are able to detect where we installed the library and add the real value to the config file (wsrep_provider) on fly, it would be even better, but I suppose it's unrealistic and/or error-prone.