build: Don't generate markdown for subprojects

Change-Id: Ib4351fc4601b00d54470d4069a78a2b23efb54aa
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/meson_options.txt b/meson_options.txt
index 929055d..aa06d2e 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -1,3 +1,4 @@
+option('generate_md', type: 'boolean', value: true)
 option('libphosphor_dbus', type: 'boolean', value: true)
 option('data_com_ibm', type: 'boolean', value: false)
 option('data_org_open_power', type: 'boolean', value: false)