docs: Override macboot/nomacboot documentation

These are two sides of the same variable (domacboot) so sphinx-argparse
generated docs are a bit confusing. Override the docs for them to clear
things up.

(cherry picked from commit cdcfaf562b)
Resolves: rhbz#1761653

docs/livemedia-creator.rst

@@ -46,6 +46,16 @@ livemedia-creator cmdline arguments
     :ref: pylorax.cmdline.lmc_parser
     :prog: livemedia-creator
 
+    --macboot : @replace
+        Make the iso bootable on UEFI based Mac systems
+
+        Default: True
+
+    --nomacboot : @replace
+        Do not create a Mac bootable iso
+
+        Default: False
+
 
 Quickstart
 ----------

docs/lorax.rst

@@ -23,6 +23,16 @@ lorax cmdline arguments
     :ref: pylorax.cmdline.lorax_parser
     :prog: lorax
 
+    --macboot : @replace
+        Make the iso bootable on UEFI based Mac systems
+
+        Default: True
+
+    --nomacboot : @replace
+        Do not create a Mac bootable iso
+
+        Default: False
+
 
 Quickstart
 ----------