docs: Adding useful rstdoc tool.

 - `rstlisttable` - Convert RST grid tables to list-tables
 - `rstreflow` - Reflow paragraphs and tables
 - `rstretable` -Transforms list tables to grid tables

Signed-off-by: Tim 'mithro' Ansell <me@mith.ro>

docs/requirements.txt

diff --git a/docs/requirements.txt b/docs/requirements.txt
index 37e7980..f20b3a6 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -16,5 +16,6 @@
 # vext.gi
 
 restructuredtext-lint
+rstdoc
 
 tabulate