testssl: add page (#4424)

pages/common/testssl.md

@@ -0,0 +1,24 @@
+# testssl
+
+> Check SSL/TLS protocols and ciphers supported by a server.
+> More information: <https://testssl.sh/>.
+
+- Test a server (run every check) on port 443:
+
+`testssl {{example.com}}`
+
+- Test a different port:
+
+`testssl {{example.com:465}}`
+
+- Only check available protocols:
+
+`testssl --protocols {{example.com}}`
+
+- Only check vulnerabilities:
+
+`testssl --vulnerable {{example.com}}`
+
+- Only check HTTP security headers:
+
+`testssl --headers {{example.com}}`