Add some docs (#198)

docs/update.md

@@ -0,0 +1,57 @@
+# Update
+
+## Make a backup
+
+Before updating, always make sure to backup the Opengist home directory, where all the data is stored. 
+
+You can do so by copying the `~/.opengist` directory (default location).
+
+```shell
+cp -r ~/.opengist ~/.opengist.bak
+```
+
+## Install the new version
+
+### With Docker
+
+Pull the last version of Opengist
+```shell
+docker pull ghcr.io/thomiceli/opengist:1
+```
+
+And restart the container, using `docker compose up -d` for example if you use docker compose.
+
+### Via binary
+
+Stop the running instance; then like your first installation of Opengist, download the archive for your system from the release page [here](https://github.com/thomiceli/opengist/releases/latest), and extract it.
+
+```shell
+# example for linux amd64
+wget https://github.com/thomiceli/opengist/releases/download/v1.6.0/opengist1.6.0-linux-amd64.tar.gz
+
+tar xzvf opengist1.6.0-linux-amd64.tar.gz
+cd opengist
+chmod +x opengist
+./opengist # with or without `--config config.yml`
+```
+
+### From source
+
+Stop the running instance; then pull the last changes from the master branch, and build the new version.
+
+```shell
+git pull
+make
+./opengist
+```
+
+## Restore the backup
+
+If you have any issue with the new version, you can restore the backup you made before updating.
+
+```shell
+rm -rf ~/.opengist
+cp -r ~/.opengist.bak ~/.opengist
+```
+
+Then run the old version of Opengist again.