De-duplicate installation instructions, and add upgrade instructions

[marclaporte]

FYI: https://en.wikipedia.org/wiki/Don't_repeat_yourself

We have info on website:

• https://github.com/cypht-org/cypht-website/blob/master/install.html
• https://github.com/cypht-org/cypht-website/blob/master/install-1x.html
• https://github.com/cypht-org/cypht-website/blob/master/install-2x.html

We have info in source code:

• https://github.com/cypht-org/cypht/blob/master/INSTALL
• https://github.com/cypht-org/cypht/blob/2.x/INSTALL (These instructions will lead you to install master instead of 2.x:)
• https://github.com/cypht-org/cypht/blob/1.4.x/INSTALL

Say I have installed Cypht 2.1.0. How do I update to Cypht 2.2.0?

[David-Muhasa]

After my analysis I propose to centralize the information in the installed Markdown file on github repository for each version. and therefore at the level of the documentation site it will be a question of writing a php script which parses the installed file for each version which is on git repository.
what do you think of this proposal before I start coding

[Baraka24]

what do you think of this proposal before I start coding

It is a good thing to have that php script and consider what @marclaporte said above:

Say I have installed Cypht 2.1.0. How do I update to Cypht 2.2.0?