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-enter.md

@@ -0,0 +1,13 @@
+# yadm-enter
+
+> Run a sub-shell with all Git variables set. This sub-shell can be used to easily interact with the local `yadm` repository using Git commands.
+> This could be useful if you are using a tool which uses Git directly.
+> More information: <https://github.com/TheLocehiliosan/yadm/blob/master/yadm.md#commands>.
+
+- Run a sub-shell with all Git variables set:
+
+`yadm enter`
+
+- Exit the sub-shell:
+
+`exit`