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Description 😯

In the official documenation of Trubudget there is an old version describing how to connect to a blockchain spinning up a slave node https://trubudget.net/docs/operation-administration/installation/connect-to-existing-node/connect-docker-compose

In the github documentation there is no documentation how to connect to a blockchain spinning up a slave node but there is a hidden section in the "create a new network" section: https://github.com/openkfw/TruBudget/blob/master/docs/operation-administration/installation/create-new-network/create-new-docker-compose.md#connect-to-an-existing-blockchain-network
This docu is NOT describing how to connect to an existing blockchain network but it's describing how to spin up a new network with 2 organizations connected.

The goal is to have 2 documentation sections synced with the Trubudget website and the github docu:

1. Create a new network
2. Connect to an existing network

Also the misleading doc section in "Create a new network" should be renamed to something like "Create a new network with 2 organizations".