mg: add page (#8441)

* mg: add page

* Fix description

* Fix example

* Compress description to one line

* Remove unnecessary comma

pages/common/mg.md

@@ -0,0 +1,20 @@
+# mg
+
+> A small, fast, and portable text editor based on `emacs`.
+> More information: <https://github.com/hboetes/mg>.
+
+- Open a file for editing:
+
+`mg {{path/to/file}}`
+
+- Open a file at a specified line number:
+
+`mg +{{line_number}} {{path/to/file}}`
+
+- Open files in a read-only mode:
+
+`mg -R {{path/to/file1 path/to/file2 ...}}`
+
+- Disable `~` backup files while editing:
+
+`mg -n {{path/to/file}}`