Make more clear about readme parser warnings

[ernilambar]

If there are warnings returned from the Parser, we display message like this:

The following readme parser warnings were detected: tested_header_ignored, requires_php_header_ignored

Message here is not quite clear. May be we could display more clearer messages for each warnings.

Existing warnings in the Parser:

• contributor_ignored
• requires_php_header_ignored
• tested_header_ignored
• requires_header_ignored