speedtest-cli: add page (#1794)

pages/common/speedtest-cli.md

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+# speedtest-cli
+
+> Command line interface for testing internet bandwidth using speedtest.net.
+
+- Run a speed test:
+
+`speedtest-cli`
+
+- Run a speed test and generate a sharable result picture:
+
+`speedtest-cli --share`
+
+- Print a list of all speedtest.net servers, sorted by distance, to file:
+
+`speedtest-cli --list > speedtest_servers.txt`
+
+- Run a speed test to the given speedtest.net server id:
+
+`speedtest-cli --server {{server_id}}`