Documentation tips

## Change an URL in all files  with Perl

For example this url "https://docs.kde.org/trunk5/en/kdeedu/marble/index.html" is not working anymore, we want to redirect to "https://marble.kde.org/" which is working.

Perl syntax is `perl -pi -e 's/before/after/g' file`

So we need to use that for several files:
- English quickstart
- English overview
- translated quickstarts and overviews

To fix the url in English files, do the following :

```perl -pi -e 's/docs\.kde\.org\/trunk5\/en\/kdeedu\/marble\/index.html/marble\.kde\.org/' doc/quickstart/*```

```perl -pi -e 's/docs\.kde\.org\/trunk5\/en\/kdeedu\/marble\/index.html/marble\.kde\.org/' doc/overview/*```

For the translations do this:

```perl -pi -e 's/docs\.kde\.org\/trunk5\/en\/kdeedu\/marble\/index.html/marble\.kde\.org/' locale/*/LC_MESSAGES/quickstart/*```

```perl -pi -e 's/docs\.kde\.org\/trunk5\/en\/kdeedu\/marble\/index.html/marble\.kde\.org/' locale/*/LC_MESSAGES/overview/*```