msgfmt, msgunfmt: add page (#13809)

Co-authored-by: Sebastiaan Speck <12570668+sebastiaanspeck@users.noreply.github.com>
Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

pages/common/msgunfmt.md

@@ -0,0 +1,12 @@
+# msgunfmt
+
+> Decompile message catalog from the binary format.
+> More information: <https://www.gnu.org/software/gettext/manual/html_node/msgunfmt-Invocation.html>.
+
+- Output conversion:
+
+`msgunfmt {{path/to/file.mo}}`
+
+- Convert a `.mo` file to a `.po` file:
+
+`msgunfmt {{path/to/file.mo}} > {{path/to/file.po}}`