Update markdown docs to specify --local for the local devserver
If the devserver is run locally following the instructions on
https://skia.org/dev/tools/markdown, you'll get an error about influxdb.
It looks like an influxdb username/password is required but using
--local works around this issue.
-------------------8<-------------------
$ ./bin/docserver --preview
E0703 19:33:31.510379 30448 common.go:37] Initializing logserver for log level ERROR.
F0703 19:33:31.516750 30448 common.go:63] metadata.Get() failed to make HTTP request for influxdb_name: Get http://metadata/computeMetadata/v1/project/attributes/influxdb_name: dial tcp: lookup metadata: no such host
goroutine 1 [running]:
github.com/skia-dev/glog.stacks(0x772300, 0x0, 0x0, 0x0)
/src/github.com/skia-dev/glog/glog.go:769 +0xb8
github.com/skia-dev/glog.(*loggingT).output(0x756000, 0xc800000003, 0xc820136000, 0x73613e, 0x9, 0x3f, 0x0)
/src/github.com/skia-dev/glog/glog.go:720 +0x259
github.com/skia-dev/glog.(*loggingT).printDepth(0x756000, 0x3, 0x1, 0xc8200dde28, 0x1, 0x1)
/src/github.com/skia-dev/glog/glog.go:649 +0x1b8
github.com/skia-dev/glog.(*loggingT).print(0x756000, 0x3, 0xc8200dde28, 0x1, 0x1)
/src/github.com/skia-dev/glog/glog.go:640 +0x50
github.com/skia-dev/glog.Fatal(0xc8200dde28, 0x1, 0x1)
/src/github.com/skia-dev/glog/glog.go:1128 +0x49
go.skia.org/infra/go/common.StartMetrics2(0x5103e0, 0x9, 0xc820104400, 0xc820104430, 0xc820104450, 0xc820104470, 0xc8200dde00)
/src/go.skia.org/infra/go/common/common.go:63 +0x192
go.skia.org/infra/go/common.InitWithMetrics2(0x5103e0, 0x9, 0xc820104400, 0xc820104430, 0xc820104450, 0xc820104470, 0xc820104498)
/src/go.skia.org/infra/go/common/common.go:48 +0x65
main.main()
/src/skia.googlesource.com/buildbot.git/doc/go/docserver/main.go:183 +0x95
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GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2118113002
NOTRY=true
DOCS_PREVIEW= https://skia.org/?cl=2118113002
Review-Url: https://codereview.chromium.org/2118113002
48898561db
