[DOCS] Split long lines in Docker TLS getting-started snippet

and add warning for Windows users not using
PowerShell (e.g. `cmd.exe`) to remove the `\` character and join
lines.

Also fix trailing whitespace character in link back to `docker.asciidoc`.

Relates elastic/x-pack-elasticsearch#2999

Original commit: elastic/x-pack-elasticsearch@fe1c5dbc11

docs/en/security/securing-communications/configuring-tls-docker.asciidoc

@@ -178,8 +178,14 @@ curl --cacert certs/ca/ca.crt -u elastic:PleaseChangeMe https://localhost:9200
 all users:
 +
 --
+WARNING: Windows users not running PowerShell will need to remove `\` and join lines in the snippet below.
 ["source","sh"]
 ----
-docker exec es01 /bin/bash -c "bin/x-pack/setup-passwords auto --batch -Expack.ssl.certificate=x-pack/certificates/es01/es01.crt -Expack.ssl.certificate_authorities=x-pack/certificates/ca/ca.crt -Expack.ssl.key=x-pack/certificates/es01/es01.key --url https://localhost:9200"
+docker exec es01 /bin/bash -c "bin/x-pack/setup-passwords \
+auto --batch \
+-Expack.ssl.certificate=x-pack/certificates/es01/es01.crt \
+-Expack.ssl.certificate_authorities=x-pack/certificates/ca/ca.crt \
+-Expack.ssl.key=x-pack/certificates/es01/es01.key \
+--url https://localhost:9200"
 ----
 --