Add reference doc regen instructions

tools/luals-gendoc/README.md

@@ -0,0 +1,20 @@
+# Prerequisites
+
+ - lua-language-server
+ - a Lua interpreter version >= 5.2
+
+# Regenerating the Lua reference docs
+
+1. Invoke `lua-language-server` to parse our stubs, generating json output:
+
+```
+$ lua-language-server --doc=../../luals-stubs
+```
+
+2. The output will include the path to the raw json data. This will be a path like '/home/jacqueline/Development/lua-language-server/log/doc.json'. Pipe this file to `gendoc.lua`. The output will be quite long; consider piping to less for testing.
+
+```
+$ cat /home/jacqueline/Development/lua-language-server/log/doc.json | ./gendoc.lua | less
+```
+
+3. If updating the public-facing docs on cooltech.zone, place the resulting output in 'content/tangara/docs/lua/reference.txt'.