Added steps to configure appservice webhooks in the dimension manager.

This fixes an incorrect indentation in the database specification for
appservice-irc which caused matrix-appservice-irc to refuse to start
with the remarkably unhelpful error message:

```
ERROR:CLI Failed to run bridge.
```

This also updates doc links to the new matrixdotorg repo because the
tedomum repo contains out-of-date documentation.

Related to #339 (Github Pull Request).

Fixed small typo, added an extra note on how to use the ansible docker image when not using a ssh key for authentication

typographical error

Don't mention systemd-journald adjustment anymore, because
we've changed log levels to WARNING and Synapse is not chatty by default
anymore.

The "excessive log messages may get dropped on CentOS" issue no longer
applies to most users and we shouldn't bother them with it.

Feel free to reword but we have had a couple of issues created now asking about Raspberry Pi support.

s/type-bind/type=bind/g

Fixes #255 (Github Issue).