web-search: add README (#7203)

plugins/web-search/README.md

+# web-search plugin
+
+This plugin adds aliases for searching with Google, Wiki, Bing, YouTube and other popular services.
+
+Open your `~/.zshrc` file and enable the `web-search` plugin:
+
+```zsh
+plugins=( ... web-search)
+```
+
+## Usage
+
+You can use the `web-search` plugin in these two forms:
+
+* `web_search <context> <term> [more terms if you want]`
+* `<context> <term> [more terms if you want]`
+
+For example, these two are equivalent:
+
+```zsh
+$ web_search google oh-my-zsh
+$ google oh-my-zsh
+```
+
+Available search contexts are:
+
+| Context               | URL                                      |
+|-----------------------|------------------------------------------|
+| `bing`                | `https://www.bing.com/search?q=`         |
+| `google`              | `https://www.google.com/search?q=`       |
+| `yahoo`               | `https://search.yahoo.com/search?p=`     |
+| `ddg` or `duckduckgo` | `https://www.duckduckgo.com/?q=`         |
+| `sp` or `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=`            |
+| `ecosia`              | `https://www.ecosia.org/search?q=`       |
+| `goodreads`           | `https://www.goodreads.com/search?q=`    |
+| `qwant`               | `https://www.qwant.com/?q=`              |
+
+Also there are aliases for bang-searching DuckDuckGo:
+
+| Context   | Bang  |
+|-----------|-------|
+| `wiki`    | `!w`  |
+| `news`    | `!n`  |
+| `youtube` | `!yt` |
+| `map`     | `!m`  |
+| `image`   | `!i`  |
+| `ducky`   | `!`   |