doc: move README.falcon to HTML

Move the Falcon mode documentation to HTML.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/develop/index.rst b/doc/develop/index.rst
index ddbf8da..263d404 100644
--- a/doc/develop/index.rst
+++ b/doc/develop/index.rst
@@ -45,6 +45,7 @@
    printf
    smbios
    spl
+   falcon
    uefi/index
    vbe
    version