c-submode-indicators: docstring please

[Glenn Morris]

c-submode-indicators could use a docstring.

When I see "AWK/l" in the modeline, I wonder what the "/l" means.
Mousing over it tells me to use mouse-2 for minor mode help. But then
I just get "c-submode-indicators: Not documented as a variable"; and I
have to dig around in the cc-mode info pages to try and find it (and
it has no index entry).

TIA.