[ENHANCEMENT] ibus-table should have a way to display help for tables

[mike-fabian]

Recently tones were added to the jyutping table:

mike-fabian/ibus-table-chinese#6

The keys to type the tones were added according to:

https://github.com/rime/rime-cantonese/blob/main/README-en.md#tonal-markers

1. v: High level, e.g. siv → 詩; High level checked, e.g. sikv → 色
2. x: Medium rising, e.g. six → 史
3. q: Medium level, e.g. siq→ 試; Medium level checked, e.g. sekq → 錫
4. vv: Low falling, e.g. sivv → 時
5. xx: Low rising, e.g. sixx → 市
6. qq: Low level, e.g. siqq→ 事; Low level checked, e.g. sikqq → 食

A new user of the jyutping table might not know that tones are available and how to type them.

So it would be useful if the setup tool of ibus-table had some way to display some help about the table used.

Maybe a help file could be added where the table sources are:

jyuping.txt <- the actual table source
jyutping.help <- some file describing what the table does and how to use it

and for each table which has such a help file offer to display the help in the setup tool