add missing <head>, <body>, and/or <html> tags

show how Got's own repository can be cloned with got(1) if already installed

clarify which operating systems our release installation instructions apply to

portable: mention Github read-only clone Mention that got-portable has a read-only clone on Github, used for CI purposes.

publish got-portable 0.60 Publish the first version of -portable.

link to got-portable repository mirrors

add a page for the portable version