docs: add section about logging

docs/source/usage/index.md

@@ -13,6 +13,7 @@ In this section, we will show the fundamentals of how to work with primap2 data.
 select_and_view
 store_and_load
 add_and_overwrite
+logging
 merge
 skipna
 downscaling

docs/source/usage/logging.md

@@ -0,0 +1,66 @@
+---
+jupytext:
+  formats: md:myst
+  text_representation:
+    extension: .md
+    format_name: myst
+    format_version: 0.13
+    jupytext_version: 1.16.4
+kernelspec:
+  display_name: Python 3 (ipykernel)
+  language: python
+  name: python3
+---
+# Log messages
+
+Many primap2 functions emit log messages, which have an associated severity.
+The severities we use are shown in the table.
+
+| severity | used for                                                                         | default |
+|----------|----------------------------------------------------------------------------------|---------|
+| debug    | useful for understanding what functions do internally                            | ✗       |
+| info     | noteworthy information during normal processing                                  | ✓       |
+| warning  | problems which are not necessarily fatal, but should be acknowledged by the user | ✓       |
+| error    | problems which need to be solved by the user                                     | ✓       |
+
+As noted, by default `debug` messages are not shown, all other messages are shown.
+
+## Changing what is shown
+
+As said, by default `debug` messages are not shown, as you can see here:
+
+```{code-cell} ipython3
+import primap2
+import sys
+
+from loguru import logger
+
+logger.debug("This message will not be shown")
+logger.info("This message will be shown")
+```
+
+To change this, remove the standard logger and add a new logger:
+
+```{code-cell} ipython3
+logger.remove()
+logger.add(sys.stderr, level="DEBUG")
+
+logger.debug("Now you see debug messages")
+logger.info("You still also see info messages")
+```
+
+Instead of showing more, you can also show less:
+
+```{code-cell} ipython3
+logger.remove()
+logger.add(sys.stderr, level="WARNING")
+
+logger.debug("You don't see debug messages")
+logger.info("You also don't see info messages")
+logger.warning("But you do see all warnings")
+```
+
+## Advanced usage
+
+It is also possible to log to a file or add more information to the logs. See the
+[loguru documentation](https://loguru.readthedocs.io/) for details.