doc: fix spaces in testpmd flow syntax

In flow syntax documentation, there is example for create pattern
template.

Before the example, miss a blank line causing it to look regular bold
text.
In addition, inside the example, it uses tab instead of spaces which
expand the indentation in one line.

This patch adds the blank line and replaces tab with spaces.

Fixes: 04cc665fab ("app/testpmd: add flow template management")
Cc: stable@dpdk.org

Signed-off-by: Michael Baum <michaelba@nvidia.com>
Reviewed-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Yuying Zhang <yuying.zhang@intel.com>

doc/guides/testpmd_app_ug/testpmd_funcs.rst

@@ -2894,9 +2894,10 @@ following sections.
        [meters_number {number}] [flags {number}]
 
 - Create a pattern template::
+
    flow pattern_template {port_id} create [pattern_template_id {id}]
        [relaxed {boolean}] [ingress] [egress] [transfer]
-	   template {item} [/ {item} [...]] / end
+       template {item} [/ {item} [...]] / end
 
 - Destroy a pattern template::