Installation instructions on website do not account for `git clone`

[al0f]

Hi, All,

Recently, I tried compiling enigma from source. The instructions at 
https://www.nongnu.org/enigma/download.html#compilation work to compile 
enigma from a source tarball, however when compiling from a freshly 
clone git repository, the `configure` script does not exist, and running 
`./autogen.sh` is needed to generate it. Could you please update the 
instructions on the site to include the case when a `git clone` is used 
to download the source?

Regards,

al0f