Update homeserver.yaml to keep up with Synapse v1.40.0

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1225

roles/matrix-synapse/templates/synapse/homeserver.yaml.j2

@@ -732,6 +732,48 @@ caches:
 
 ## Database ##
 
+# The 'database' setting defines the database that synapse uses to store all of
+# its data.
+#
+# 'name' gives the database engine to use: either 'sqlite3' (for SQLite) or
+# 'psycopg2' (for PostgreSQL).
+#
+# 'txn_limit' gives the maximum number of transactions to run per connection
+# before reconnecting. Defaults to 0, which means no limit.
+#
+# 'args' gives options which are passed through to the database engine,
+# except for options starting 'cp_', which are used to configure the Twisted
+# connection pool. For a reference to valid arguments, see:
+#   * for sqlite: https://docs.python.org/3/library/sqlite3.html#sqlite3.connect
+#   * for postgres: https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-PARAMKEYWORDS
+#   * for the connection pool: https://twistedmatrix.com/documents/current/api/twisted.enterprise.adbapi.ConnectionPool.html#__init__
+#
+#
+# Example SQLite configuration:
+#
+#database:
+#  name: sqlite3
+#  args:
+#    database: /path/to/homeserver.db
+#
+#
+# Example Postgres configuration:
+#
+#database:
+#  name: psycopg2
+#  txn_limit: 10000
+#  args:
+#    user: synapse_user
+#    password: secretpassword
+#    database: synapse
+#    host: localhost
+#    port: 5432
+#    cp_min: 5
+#    cp_max: 10
+#
+# For more information on using Synapse with Postgres,
+# see https://matrix-org.github.io/synapse/latest/postgres.html.
+#
 database:
   # The database engine name
   name: "psycopg2"