Merge branch 'readme' into 'master'

Readme updates

See merge request Librem5/squeekboard!281

HACKING.md

@@ -25,7 +25,7 @@ sudo apt-get -y build-dep .
 ```
 
 For an explicit list of dependencies check the `Build-Depends` entry in the
-[debian/control][] file.
+[`debian/control`](./debian/control) file.
 
 Testing
 -------
@@ -62,6 +62,24 @@ $ gsettings set org.gnome.desktop.input-sources sources "[('xkb', 'us'), ('xkb',
 Coding
 ------
 
+### Project structure
+
+Rust modules should be split into 2 categories: libraries, and user interface. They differ in the way they do error handling.
+
+Libraries should:
+
+- not panic due to external surprises, only due to internal inconsistencies
+- pass errors and surprises they can't handle to the callers instead
+- not silence errors and surprises
+
+User interface modules should:
+
+- try to provide safe values whenever they encounter an error
+- do the logging
+- give libraries the ability to report errors and surprises (e.g. via giving them loggers)
+
+### Style
+
 Code submitted should roughly match the style of surrounding code. Things that will *not* be accepted are ones that often lead to errors:
 
 - skipping brackets `{}` after every `if()`, `else`, and similar
@@ -122,6 +140,8 @@ sh /source_path/cargo.sh test
 
 ### Cargo dependencies
 
+All Cargo dependencies must be selected in the version available in PureOS, and added to the file `debian/control`. Please check with https://software.pureos.net/search_pkg?term=librust .
+
 Dependencies must be specified in `Cargo.toml` with 2 numbers: "major.minor". Since bugfix version number is meant to not affect the interface, this allows for safe updates.
 
 `Cargo.lock` is used for remembering the revisions of all Rust dependencies. It should be updated often, preferably with each bugfix revision, and in a commit on its own: