Generate valid README.md

[tudorconstantin]

I signep up for the Perl Pull-Request challenge and perlbrew is the module I got for March.
The biggest improvement I could think of is the documentation format, because:

• github favors Markdown for documentation
• an HTML README is much easier to read than the text version
• with every fork the project gets, more backlinks to important perl stuff like perlbrew, metacpan are created

[coveralls]

Coverage remained the same at 82.48% when pulling 535fc6d on tudorconstantin:generate_valid_README_md into 1495d17 on gugod:develop.

[coveralls]

Coverage increased (+0.08%) to 82.56% when pulling 535fc6d on tudorconstantin:generate_valid_README_md into 1495d17 on gugod:develop.