Include hint for PostgreSQL pw in self-hosted instruction

[macntech]

In the self hosted instruction under https://cusdis.com/doc#/self-host/vercel we should include a hint for PostgreSQL passwort that it should not contain any special character, especially '@'. This character will lead to build fail on Vercel as the @ will be interpreted as host prefix.

Example: Postgresql passwort 12345w@erf in connection string will lead to error:

Another option would be to give users the hint to encode special character in the connection string as per https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-CONNSTRING

Example: Postgresql passwort '12345w@erf' would be '12345w%40erf' in the connection string.

We could also do the character substitution in the execution code.

[djyde]

Thank you macntech. Could you help us update the doc?