dos/{loadfix, loadhigh, md, mem, mixer}: add page (#20863)

* LOADFIX: add page

Added documentation for LOADFIX command usage in DOS.

* LOADHIGH: add page

* MD: add page

* MEM: add page

* MIXER: add page

Added documentation for the MIXER command with usage examples.

* Update pages/dos/loadhigh.md

Co-authored-by: Managor <42655600+Managor@users.noreply.github.com>

* Update pages/dos/mixer.md

Co-authored-by: Managor <42655600+Managor@users.noreply.github.com>

* Update link for MD command documentation

* Update MEM command documentation link

* Fix LOADHIGH documentation link

Updated the LOADHIGH command documentation with a new link.

* Update LOADFIX documentation link for accuracy

* Update pages/dos/loadfix.md

Co-authored-by: Ivan Baluta <ivanbaluta.dev@gmail.com>

* Update pages/dos/loadfix.md

Co-authored-by: Ivan Baluta <ivanbaluta.dev@gmail.com>

* Update pages/dos/loadfix.md

Co-authored-by: Ivan Baluta <ivanbaluta.dev@gmail.com>

* Update pages/dos/md.md

Co-authored-by: Ivan Baluta <ivanbaluta.dev@gmail.com>

---------

Co-authored-by: Managor <42655600+Managor@users.noreply.github.com>
Co-authored-by: Ivan Baluta <ivanbaluta.dev@gmail.com>

pages/dos/loadfix.md

@@ -0,0 +1,16 @@
+# LOADFIX
+
+> Reduce available conventional memory for old programs (default: 64KB).
+> More information: <https://www.dosbox.com/wiki/LOADFIX>.
+
+- Start a program with 64KB allocated memory:
+
+`LOADFIX {{program}}`
+
+- Load with custom KB reduction (1-1024):
+
+`LOADFIX -{{32}} {{program}}`
+
+- Free all previously allocated memory:
+
+`LOADFIX -f`

pages/dos/loadhigh.md

@@ -0,0 +1,8 @@
+# LOADHIGH
+
+> Load program into upper memory (requires `xms=true`, `umb=true`).
+> More information: <https://www.dosbox.com/wiki/Commands#LOADHIGH>.
+
+- Load program into upper memory:
+
+`LOADHIGH {{program}}`

pages/dos/md.md

@@ -0,0 +1,8 @@
+# MD
+
+> Make a directory.
+> More information: <https://www.dosbox.com/wiki/Commands#MD>.
+
+- Create directory:
+
+`MD {{path/to/directory}}`

pages/dos/mem.md

@@ -0,0 +1,8 @@
+# MEM
+
+> Display free memory info.
+> More information: <https://www.dosbox.com/wiki/Commands#MEM>.
+
+- Display free memory:
+
+`MEM`

pages/dos/mixer.md

@@ -0,0 +1,28 @@
+# MIXER
+
+> Display/set sound levels.
+> More information: <https://www.dosbox.com/wiki/MIXER>.
+
+- Display current volumes:
+
+`MIXER`
+
+- Set master volume (left:right percentages):
+
+`MIXER master {{80}}:{{80}}`
+
+- Set Sound Blaster volume in decibels:
+
+`MIXER sb d{{10}}:d{{10}}`
+
+- Set GUS left channel only:
+
+`MIXER gus {{50}}`
+
+- Set volumes without displaying result:
+
+`MIXER gus {{40}}:{{40}} /NOSHOW`
+
+- List available MIDI devices (Windows only):
+
+`MIXER /LISTMIDI`