cgi: add some docs.

extra/cgi/cgi-docs.factor

@@ -10,3 +10,16 @@ HELP: <cgi-form>
 HELP: <cgi-simple-form>
 { $values { "assoc" assoc } }
 { $description "Parse a CGI request into an " { $link assoc } ". Only the first parameter is kept, if multiple parameters are passed." } ;
+
+ARTICLE: "cgi" "CGI (Common Gateway Interface)"
+"The " { $vocab-link "cgi" } " can be used to parse a CGI request:"
+{ $subsections
+    <cgi-form>
+    <cgi-simple-form>
+}
+{ $heading "Troubleshooting" }
+"If the CGI script leaves elements on the stack, you'll get an error like the following (after running all of the code in your script):"
+$nl
+{ $snippet "Quotation called with wrong stack effect effect ( -- )" } ;
+
+ABOUT: "cgi"