zsh-comp: explain how to use for non-global install
adding a% default context[0;1mdiff -r cf9f4ba66af2 a[0m[0;31;1m--- a/a[0m[0;32;1m+++ b/a[0m[0;35m@@ -2,7 +2,7 @@[0m c a a[0;31m-b[0m[0;32m+dd[0m a a c% --unified=2[0;1mdiff -r cf9f4ba66af2 a[0m[0;31;1m--- a/a[0m[0;32;1m+++ b/a[0m[0;35m@@ -3,5 +3,5 @@[0m a a[0;31m-b[0m[0;32m+dd[0m a a