[PATCH v2] INSTALL: note on using Asciidoctor to build doc

[Bagas Sanjaya <bagasdotme@gmail.com>]

Note on using Asciidoctor to build documentation suite.

Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
---

 Changes from v1:
   * Apply suggestions from Junio:
     * Place on the same paragraph as asciidoc version requirement
     * Reword
   * Mention Asciidoctor minimum version required for building to 1.5
     (as suggested by brian m. carlson)

 INSTALL | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/INSTALL b/INSTALL
index 8474ad01bf..66389ce059 100644
--- a/INSTALL
+++ b/INSTALL
@@ -197,7 +197,9 @@ Issues of note:
    Building and installing the pdf file additionally requires
    dblatex.  Version >= 0.2.7 is known to work.
 
-   All formats require at least asciidoc 8.4.1.
+   All formats require at least asciidoc 8.4.1. Alternatively, you can
+   use Asciidoctor (requires Ruby) by passing USE_ASCIIDOCTOR=YesPlease
+   to make. You need at least Asciidoctor version 1.5.
 
    There are also "make quick-install-doc", "make quick-install-man"
    and "make quick-install-html" which install preformatted man pages
-- 
2.25.1