docs(readme): fix public ip echo custom url prefix url:https:// instead of https://

Author: qdm12

README.md

@@ -282,7 +282,7 @@ You can otherwise customize it with the following:
   - `nnev` using [https://ip.nnev.de](https://ip.nnev.de)
   - `wtfismyip` using [https://wtfismyip.com/text](https://wtfismyip.com/text)
   - `seeip` using [https://api.seeip.org](https://api.seeip.org)
-  - You can also specify an HTTPS URL such as `https://ipinfo.io/ip`
+  - You can also specify an HTTPS URL with prefix `url:` for example `url:https://ipinfo.io/ip`
 - `PUBLICIPV4_HTTP_PROVIDERS` gets your public IPv4 address only. It can be one or more of the following:
   - `ipleak` using [https://ipv4.ipleak.net/json](https://ipv4.ipleak.net/json)
   - `ipify` using [https://api.ipify.org](https://api.ipify.org)
@@ -291,7 +291,7 @@ You can otherwise customize it with the following:
   - `nnev` using [https://ip4.nnev.de](https://ip4.nnev.de)
   - `wtfismyip` using [https://ipv4.wtfismyip.com/text](https://ipv4.wtfismyip.com/text)
   - `seeip` using [https://ipv4.seeip.org](https://ipv4.seeip.org)
-  - You can also specify an HTTPS URL such as `https://ipinfo.io/ip`
+  - You can also specify an HTTPS URL with prefix `url:` for example `url:https://ipinfo.io/ip`
 - `PUBLICIPV6_HTTP_PROVIDERS` gets your public IPv6 address only. It can be one or more of the following:
   - `ipleak` using [https://ipv6.ipleak.net/json](https://ipv6.ipleak.net/json)
   - `ipify` using [https://api6.ipify.org](https://api6.ipify.org)
@@ -300,7 +300,7 @@ You can otherwise customize it with the following:
   - `nnev` using [https://ip6.nnev.de](https://ip6.nnev.de)
   - `wtfismyip` using [https://ipv6.wtfismyip.com/text](https://ipv6.wtfismyip.com/text)
   - `seeip` using [https://ipv6.seeip.org](https://ipv6.seeip.org)
-  - You can also specify an HTTPS URL such as `https://ipinfo.io/ip`
+  - You can also specify an HTTPS URL with prefix `url:` for example `url:https://ipinfo.io/ip`
 - `PUBLICIP_DNS_PROVIDERS` gets your public IPv4 address only or IPv6 address only or one of them (see #136). It can be one or more of the following:
   - `cloudflare`
   - `opendns`