Doc: sync from Wiki, generate HTML

Additions:
 - Installation/Download: how to get Shaarli
 - Community software: ShaarliOS app

Modifications:
 - Installation/Server requirements: PHP 5.4 EOL, PHP 7 announcements
 - Installation/Server configuration: improve Nginx security
 - Troubleshooting: PHP sessions on `free.fr`

Signed-off-by: VirtualTam <virtualtam@flibidi.net>

1 files changed, 31 insertions, 0 deletions

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+#Download
+## Get Shaarli!
+### Latest stable revision
+This revision has been [released](https://github.com/shaarli/Shaarli/releases) and tested.[](.html)
+
+#### Clone with Git (recommended)
+```bash
+$ git clone https://github.com/shaarli/Shaarli.git -b stable shaarli
+```
+
+#### Download as an archive
+```bash
+$ wget https://github.com/shaarli/Shaarli/archive/stable.zip
+$ unzip stable.zip
+$ mv Shaarli-stable shaarli
+```
+
+Tarballs are also available:
+```bash
+$ wget https://github.com/shaarli/Shaarli/archive/stable.tar.gz
+$ tar xvf stable.tar.gz
+$ mv Shaarli-stable shaarli
+```
+
+### Development (mainline)
+_Use at your own risk!_
+
+To get the latest changes:
+```bash
+$ git clone https://github.com/shaarli/Shaarli.git shaarli
+```