vegeta: add vegeta http load testing document. (#2519)

Describe one example for each vegeta load testing case. One simple
attack, one with a rate, one attack with a report,
one with a report as a plot and finally one with a configuration file.

Fixes: https://github.com/tldr-pages/tldr/issues/2309
Refs: https://github.com/tsenart/vegeta

pages/common/vegeta.md

@@ -0,0 +1,28 @@
+# vegeta
+
+> Vegeta is both a command line utility and a library for HTTP load testing.
+> See also `ab`.
+
+- Launch an attack lasting 30 seconds:
+
+`echo "{{GET https://example.com}}" | vegeta attack -duration={{30s}}`
+
+- Launch an attack on a server with a self-signed https certificate:
+
+`echo "{{GET https://example.com}}" | vegeta attack -insecure -duration={{30s}}`
+
+- Launch an attack with a rate of 10 requests per second:
+
+`echo "{{GET https://example.com}}" | vegeta attack -duration={{30s}} -rate={{10}}`
+
+- Launch an attack and display for a report:
+
+`echo "{{GET https://example.com}}" | vegeta attack -duration={{30s}} | vegeta report`
+
+- Launch an attack and plot the results on a graph (latency against time):
+
+`echo "{{GET https://example.com}}" | vegeta attack -duration={{30s}} | vegeta plot > {{path/to/results.html}}`
+
+- Launch an attack against multiple URLs from a file:
+
+`vegeta attack -duration={{30s}} -targets=requests.txt | vegeta report`