Documentation suggestion for external users

[lydiayliu]

• recommended Python version / range of versions
• instructions for downloading specific versions of Ensembl release that is not the latest on the FTP download page

[lydiayliu]

In the Quick Start guide, the last two sections are slightly out of date
For example:

• missing \ at end of line in the parseVEP example and the callPeptide example
• vep-txt
• output-prefix
• input-variant
• vep.tvf
• callPeptide is now callVariant