Document and end-user-simplify the perltags and autocomplete featureset

[tsee]

Currently, we support autocompletion via ctags-like files generated by the Perl::Tags module. You can set the "perltags" file in the preferences since recently. You can use all this to autocomplete class names, some variables and method calls. It's used to implement the advanced form of "jump-to-method-declaration".

Users won't use this unless we make it really easy. Specifically, we (probably) can't ship a default perltags file with Padre since it contains absolute file names.

[bowtie]

this is an example of something we should do by default

ie fill in the preferences if ctags found locally