I have vim with airline, that tells me which mode I am in. I would like to change it so that rather than the whole word it just displays the first letter. So N, I or V. Although I can find instructions for changing colours of the mode indicator, I can't find the command to add to my .vimrc that will change the text. What do I add?
I don't use the plugin, but was able to locate the information in its help almost immediately.
You're looking for the g:airline_mode_map configuration; the example even does exactly what you're asking for (single mode letters), so just copy-and-paste the fragment into your ~/.vimrc!
Also, I would recommend to open an issue / ask the plugin author next time. It might take a bit longer until you get an answer, but it alerts the author about things that aren't yet documented or are hard to find in the documentation, so he can improve it.