runtime(doc): Clarify list-concatenation a bit more Commit: https://github.com/vim/vim/commit/c9c2e2d2ff4429a6b5876ee919f15c1dc0018e86 Author: qeatzy <qeatzy@users.noreply.github.com> Date: Wed Feb 7 17:52:25 2024 +0100 runtime(doc): Clarify list-concatenation a bit more Make doc list-concatenation more clear as for += and extend(). 1. describe `+=` for list-concatenation more accurately 2. add `extend()` example for list-concatenation 3. Fix CI errors for missing helptags reference |+=| closes: #13983 Signed-off-by: qeatzy <qeatzy@users.noreply.github.com> Signed-off-by: Christian Brabandt <cb@256bit.org>