docs: mention implicitly watched directories in documentation (#14019)

* docs: mention implicitly watched directories in documentation

Signed-off-by: Rens Groothuijsen <l.groothuijsen@alumni.maastrichtuniversity.nl>

* Add mention of atomic file renaming

Co-authored-by: Ayoub Mrini <ayoubmrini424@gmail.com>
Signed-off-by: Rens Groothuijsen <l.groothuijsen@alumni.maastrichtuniversity.nl>

---------

Signed-off-by: Rens Groothuijsen <l.groothuijsen@alumni.maastrichtuniversity.nl>
Co-authored-by: Ayoub Mrini <ayoubmrini424@gmail.com>
Co-authored-by: Björn Rabenstein <beorn@grafana.com>

docs/configuration/configuration.md

@@ -1608,7 +1608,16 @@ and serves as an interface to plug in custom service discovery mechanisms.
 
 It reads a set of files containing a list of zero or more
 `<static_config>`s. Changes to all defined files are detected via disk watches
-and applied immediately. Files may be provided in YAML or JSON format. Only
+and applied immediately. 
+
+While those individual files are watched for changes,
+the parent directory is also watched implicitly. This is to handle [atomic
+renaming](https://github.com/fsnotify/fsnotify/blob/c1467c02fba575afdb5f4201072ab8403bbf00f4/README.md?plain=1#L128) efficiently and to detect new files that match the configured globs.
+This may cause issues if the parent directory contains a large number of other files,
+as each of these files will be watched too, even though the events related
+to them are not relevant.
+
+Files may be provided in YAML or JSON format. Only
 changes resulting in well-formed target groups are applied.
 
 Files must contain a list of static configs, using these formats: