support for startpage search engine in web-search plugin (#5245)

plugins/web-search/web-search.plugin.zsh

@@ -10,6 +10,7 @@ function web_search() {
     bing        "https://www.bing.com/search?q="
     yahoo       "https://search.yahoo.com/search?p="
     duckduckgo  "https://www.duckduckgo.com/?q="
+    startpage   "https://www.startpage.com/do/search?q="
     yandex      "https://yandex.ru/yandsearch?text="
     github      "https://github.com/search?q="
     baidu       "https://www.baidu.com/s?wd="
@@ -41,6 +42,7 @@ alias bing='web_search bing'
 alias google='web_search google'
 alias yahoo='web_search yahoo'
 alias ddg='web_search duckduckgo'
+alias sp='web_search startpage'
 alias yandex='web_search yandex'
 alias github='web_search github'
 alias baidu='web_search baidu'