Obsolete installation instructions

[Ashark]

In the readme the step 2 tells:

2. Copy/move the ansible-completion.bash in your bash_completion.d
   folder (/etc/bash_completion.d, /usr/local/etc/bash_completion.dor ~/bash_completion.d).

But that path does not exist anymore. See https://archlinux.org/todo/use-usrsharebash-completioncompletions-for-package-bash-completions/

Instead, I think each *-completion.bash file except ansible-completion.bash should source the common one. I.e. include the following line after shebang:
source /usr/share/bash-completion/completions/ansible