yadm: add pages (#13920)

Co-authored-by: Sebastiaan Speck <12570668+sebastiaanspeck@users.noreply.github.com>
Co-authored-by: Wiktor Perskawiec <git@spageektti.cc>

pages/common/yadm-config.md

@@ -0,0 +1,20 @@
+# yadm-config
+
+> Pass options to `yadm`'s config file. Change the `.config` of the repository managed by `yadm`.
+> See also: <https://github.com/TheLocehiliosan/yadm/blob/master/yadm.md#configuration>.
+
+- Set or update a `yadm`'s Git configuration:
+
+`yadm config {{key.inner-key}} {{value}}`
+
+- Get a value from `yadm`'s Git configuration:
+
+`yadm config --get {{key}}`
+
+- Unset a value in `yadm`'s Git configuration:
+
+`yadm config --unset {{key}}`
+
+- List all values in `yadm`'s Git configuration:
+
+`yadm config --list`