[Docs] add usefull info to REQUIRE_SIGNIN_VIEW (#9848)

docs/content/doc/advanced/config-cheat-sheet.en-us.md

@@ -309,7 +309,7 @@ relation to port exhaustion.
 - `REQUIRE_EXTERNAL_REGISTRATION_PASSWORD`: **false**: Enable this to force externally created
    accounts (via GitHub, OpenID Connect, etc) to create a password. Warning: enabling this will
    decrease security, so you should only enable it if you know what you're doing.
-- `REQUIRE_SIGNIN_VIEW`: **false**: Enable this to force users to log in to view any page.
+- `REQUIRE_SIGNIN_VIEW`: **false**: Enable this to force users to log in to view any page or to use API.
 - `ENABLE_NOTIFY_MAIL`: **false**: Enable this to send e-mail to watchers of a repository when
    something happens, like creating issues. Requires `Mailer` to be enabled.
 - `ENABLE_BASIC_AUTHENTICATION`: **true**: Disable this to disallow authenticaton using HTTP

routers/repo/pull.go

@@ -351,7 +351,7 @@ func PrepareViewPullInfo(ctx *context.Context, issue *models.Issue) *git.Compare
 	ctx.Data["Divergence"] = divergence
 	allowUpdate, err := pull_service.IsUserAllowedToUpdate(pull, ctx.User)
 	if err != nil {
-		ctx.ServerError("GetDiverging", err)
+		ctx.ServerError("IsUserAllowedToUpdate", err)
 		return nil
 	}
 	ctx.Data["UpdateAllowed"] = allowUpdate