English install.md has incorrect python info

[gruxor]

Describe the bug The English version of install.md still says "Blade requires Python 2.7.x and does not support python3 at this time." despite the project supporting Python 3 for quite some time, from what I can see.

Additional context Sorry that this is such a small issue, I didn't think it'd be appropriate to PR it as an outside user (who hasn't even used the project yet, let alone cloned the source or anything). Thanks for the interesting tool, looking forward to using it!