Missing information on requirements for local setup

[bocytko]

Since running the linter will be required for contributions, we should be explicit about the requirements for the development environment:

$ make lint
golint -set_exit_status
make: golint: No such file or directory
make: *** [lint] Error 1

otelcol-lightstep-receiver/Makefile

Lines 35 to 37 in da12e05

	lint:
	golint -set_exit_status $(SOURCE_DIRS)
	golangci-lint run

uses at least golint and golangci-lint.

For godoc the behavior is different:

$ make godoc
go install github.com/princjef/gomarkdoc/cmd/gomarkdoc@latest
go: downloading github.com/princjef/gomarkdoc v1.1.0
go: downloading github.com/princjef/termdiff v0.1.0
[...]
go: downloading gopkg.in/warnings.v0 v0.1.2
gomarkdoc --output ./docs/receiver.md ./
make: gomarkdoc: No such file or directory
make: *** [godoc] Error 1

Despite the install step, the command was still not available. (I can build and run skipper, but have no explicit env variables set for go).