Update README.md

README.md

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 # htpdate
-a tool to synchronize system time with web servers
+
+A tool to synchronize system time with web servers.
+
+## Examples
+
+Get time from multiple URLs
+
+```bash
+htpdate www.pool.ntp.org www.openssl.org nodejs.org
+```
+
+Change default protocol to 'http'
+
+```bash
+htpdate --protocol http www.pool.ntp.org
+```
+
+Mix http url and https url
+
+```bash
+htpdate http://www.pool.ntp.org https://www.openssl.org
+```
+
+Access through a http proxy
+
+```bash
+set http_proxy=http://127.0.0.1:8118
+htpdate www.pool.ntp.org
+```
+
+
+## Usage
+`htpdate [options...] urls...`
+
+### Options
+```
+ -c, --count            The number of requests for each url
+                        Default: 4
+
+ -C, --command          Command to adjust system time, in https://day.js.org/ display format
+                        Default: '[time ]HH:mm:ss.SS[ && date ]YYYY-MM-DD'
+
+ -h, --help             This help text
+                        Default: false
+
+ -i, --interval         The minimum milliseconds between requests
+                        Default: 500
+
+ -m, --method           HTTP method
+                        Default: 'HEAD'
+
+ -p, --protocol         Use this protocol when no protocol is specified in the url
+                        Default: 'https'
+
+ -r, --redirect         If redirect responses should be followed
+                        Default: false
+
+ -s, --set              Adjust system time if necessary
+                        Default: false
+
+ -t, --threshold        At least how many milliseconds are considered to adjust system time
+                        Default: 1500
+
+ -T, --timeout
+                        Default: 6000
+
+ -u, --user-agent
+                        Default: 'htpdate/1.0.0'
+
+ -v, --version          display the version of htpdate and exit
+                        Default: false
+```