Merge branch 'mysql-to-og' into 'master'

MySQL to Postgres script

doc/update/mysql-to-postgresql.md

@@ -0,0 +1,9 @@
+# Use the shell commands below to convert a MySQL GitLab database to a PostgreSQL one.
+
+```
+git clone https://github.com/lanyrd/mysql-postgresql-converter.git
+cd mysql-postgresql-converter
+mysqldump --compatible=postgresql --default-character-set=utf8 -r databasename.mysql -u root gitlabhq_production
+python db_converter.py databasename.mysql databasename.psql
+psql -f databasename.psql -d gitlabhq_production
+```