Promtail: Fix examples how to build it (#8898)

The build flags have to be provided before the package paths.

Otherwise the `build` command fails with this error:
> malformed import path "--tags=promtail_journal_enabled": leading dash

See `go help build`:
> usage: go build [-o output] [build flags] [packages]

README.md

@@ -120,14 +120,14 @@ With Journal support on Ubuntu, run with the following commands:
 
 ```bash
 $ sudo apt install -y libsystemd-dev
-$ go build ./clients/cmd/promtail --tags=promtail_journal_enabled
+$ go build --tags=promtail_journal_enabled ./clients/cmd/promtail
 ```
 
 With Journal support on CentOS, run with the following commands:
 
 ```bash
 $ sudo yum install -y systemd-devel
-$ go build ./clients/cmd/promtail --tags=promtail_journal_enabled
+$ go build --tags=promtail_journal_enabled ./clients/cmd/promtail
 ```
 
 Otherwise, to build Promtail without Journal support, run `go build`

docs/sources/upgrading/_index.md

@@ -85,7 +85,7 @@ The go build tag `promtail_journal_enabled` should be passed to include Journal
 If you need Journal support you will need to run go build with tag `promtail_journal_enabled`:
 
 ```shell
-go build ./clients/cmd/promtail --tags=promtail_journal_enabled
+go build --tags=promtail_journal_enabled ./clients/cmd/promtail
 ```
 Introducing this tag aims to relieve Linux/CentOS users with CGO enabled from installing libsystemd-dev/systemd-devel libraries if they don't need Journal support.