add Github Pull requests rss feed (#1549)

add Github pull requests rss feed with `github/pull/{user}/{repo}` this pattern

docs/README.md

@@ -682,6 +682,8 @@ GitHub 官方也提供了一些 RSS:
 
 <route name="仓库 Issue" author="HenryQW" example="/github/issue/DIYgod/RSSHub" path="/github/issue/:user/:repo" :paramsDesc="['用户名', '仓库名']"/>
 
+<route name="仓库 Pull Requests" author="hashman" example="/github/pull/DIYgod/RSSHub" path="/github/pull/:user/:repo" :paramsDesc="['用户名', '仓库名']"/>
+
 <route name="用户" author="HenryQW" example="/github/user/followers/HenryQW" path="/github/user/followers/:user" :paramsDesc="['用户名']"/>
 
 <route name="仓库 Stars" author="HenryQW" example="/github/stars/DIYgod/RSSHub" path="/github/stars/:user/:repo" :paramsDesc="['用户名', '仓库名']"/>

lib/router.js

@@ -321,6 +321,7 @@ if (config.github && config.github.access_token) {
 }
 router.get('/github/trending/:since/:language?', require('./routes/github/trending'));
 router.get('/github/issue/:user/:repo', require('./routes/github/issue'));
+router.get('/github/pull/:user/:repo', require('./routes/github/pulls'));
 router.get('/github/user/followers/:user', require('./routes/github/follower'));
 router.get('/github/stars/:user/:repo', require('./routes/github/star'));
 router.get('/github/search/:query/:sort?/:order?', require('./routes/github/search'));

lib/routes/github/pulls.js

@@ -0,0 +1,34 @@
+const axios = require('../../utils/axios');
+const config = require('../../config');
+const md = require('markdown-it')({
+    html: true,
+});
+
+module.exports = async (ctx) => {
+    const user = ctx.params.user;
+    const repo = ctx.params.repo;
+
+    const host = `https://github.com/${user}/${repo}/pull`;
+    const url = `https://api.github.com/repos/${user}/${repo}/pulls`;
+
+    const response = await axios({
+        method: 'get',
+        url,
+        params: {
+            sort: 'created',
+            access_token: config.github.access_token,
+        },
+    });
+    const data = response.data;
+
+    ctx.state.data = {
+        title: `${user}/${repo} Pull requests`,
+        link: host,
+        item: data.map((item) => ({
+            title: item.title,
+            description: md.render(item.body) || 'No description',
+            pubDate: new Date(item.created_at).toUTCString(),
+            link: `${host}/${item.number}`,
+        })),
+    };
+};