doc add explanation missing from per context provate data
doc add explanation missing from per context provate data

Signed-off-by: Andy Green <b471f5a494de34531c9e5a6e15abda71edd49104@linaro.org>

tvanderbruggen/libwebsockets,davidgaleano/libwebsockets,tvanderbruggen/libwebsockets,tvanderbruggen/libwebsockets,tvanderbruggen/libwebsockets,tvanderbruggen/libwebsockets,davidgaleano/libwebsockets,davidgaleano/libwebsockets,davidgaleano/libwebsockets