[release-branch.go1.10] doc: add note about invalid flag errors to 1.10 release notes
[release-branch.go1.10] doc: add note about invalid flag errors to 1.10 release notes

Updates #23672
Updates #23749

Change-Id: I85b6493bd1e4095398508b7ef395c35463dfbde1
Reviewed-on: https://go-review.googlesource.com/94158
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>
(cherry picked from commit f2354d0aacdd5ce1952c5441c6a489378ccb7656)
Reviewed-on: https://go-review.googlesource.com/94655

christopher-henderson/Go