Docker compose .gitignore update (#100)

Docker compose allows override some settings in `docker-compose.yml` by
using additional file: `docker-compose.override.yml`.
This allows to hold own settings in override file which does not
conflict with updates made by pulling newer version with "git pull"
command.

This feature requires three things:
1. Creating `docker-compose.override.yml-dist` file which is a
distributed file inside repo. This file can be copied as
`docker-compose.override.yml` and modified for own needs.
2. Change in `.gitignore` file so `docker-compose.override.yml` file is
ignored, so git pull / commit will not complain about this file.
3. Modify wiki entry about setup to mention possibility to use this
method.

Closes #101

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