doc: edit version vignette

vignettes/database-versions.Rmd

@@ -16,8 +16,50 @@ knitr::opts_chunk$set(
 )
 ```
 
-```{r setup}
-library(forcis)
+The [FORCIS database](https://zenodo.org/doi/10.5281/zenodo.7390791) is regularly updated. The global structure of the `csv` files doesn't change between versions but some bugs can be fixed and new records can also be added. This is why it is **recommended to use the latest version** of the database.
+
+
+## Using the latest version
+
+The package `forcis` is designed to handle the versioning of the database on Zenodo and will inform the user if a new version is available each time he/she uses one of the `read_*_data()` functions. The following message will be displayed:
+
+```
+A newer version of the FORCIS database is available. Use 'download_forcis_db(version = NULL)' to download it.
+```
+
+As mentioned in this message, the decision to download and use the latest version of the database is left to the user.
+
+A **good practice** to ensure that the user works with the latest version of the database might be to add this line at the beginning of the script:
+
+```{r 'use-latest-version'}
+download_forcis_db(version = NULL, ...)
+```
+
+Note that the FORCIS database is saved in `forcis-db/version-99/`, where `99` is the label of the version. If you regularly download the new versions, the content of the folder `forcis-db/` can increase with time and it can be interesting to manually delete the folder of the previous versions.
+
+
+## Using a specific version
+
+If for some reasons the user wants to freeze the version he/she uses, it is possible to disable this message by setting the argument `check_for_update` to `FALSE` in the `read_*_data()` functions.
+
+It is also possible to disable this message globally with the following line:
+
+```{r 'disable-message'}
+options(check_for_update = FALSE)
+```
+
+The package `forcis` "knows" which version of the database you used last time. A hidden file `.forcis` is created/updated each time the function `download_forcis_db()` or `read_*_data()` is called. This hidden file contains one line:
+
+```
+FORCIS_VERSION=99
+```
+
+Note that this hidden file is used by some functions of the `forcis` package. User doesn't have to edit it by hand.
+
+If you want to be sure to use a specific version of the database, you can use the argument `version` of the `read_*_data()` functions, or use the following line:
+
+```{r 'freeze-version'}
+options(forcis_version = "99")
 ```
 
-Work in progress...
+But again, it is **recommended to use the latest version** of the database.