Added env example and unfollow users who aren't following you example

.env.example

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+IG_USERNAME = null
+IG_PASSWORD = null
+# Uncomment this to set a proxy
+# IG_PROXY=

examples/unfollow-users.example.ts

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+/* tslint:disable:no-console */
+/*
+  This is an example of unfollowing users who aren't following you back.
+  Thanks to the developers for this great package.
+ */
+import 'dotenv/config';
+import { IgApiClient, Feed } from '../src';
+
+const ig = new IgApiClient();
+
+ig.state.generateDevice(process.env.IG_USERNAME);
+
+(async () => {
+  await ig.account.login(process.env.IG_USERNAME, process.env.IG_PASSWORD);
+
+  const followersFeed = ig.feed.accountFollowers(ig.state.cookieUserId);
+  const followingFeed = ig.feed.accountFollowing(ig.state.cookieUserId);
+
+  const followers = await getAllItemsFromFeed(followersFeed);
+  const following = await getAllItemsFromFeed(followingFeed);
+  // Making a new map of users username that follow you.
+  const followersUsername = new Set(followers.map(({ username }) => username));
+  // Filtering through the ones who aren't following you.
+  const notFollowingYou = following.filter(({ username }) => !followersUsername.has(username));
+  // Looping through and unfollowing each user
+  for (const user of notFollowingYou) {
+    await ig.friendship.destroy(user.pk);
+    console.log(`unfollowed ${user.username}`);
+    /*
+        Time, is the delay which is between 1 second and 7 seconds.
+        Creating a promise to stop the loop to avoid api spam
+     */
+    const time = Math.round(Math.random() * 6000) + 1000;
+    await new Promise(resolve => setTimeout(resolve, time));
+  }
+})();
+
+/**
+ * Source: https://github.com/dilame/instagram-private-api/issues/969#issuecomment-551436680
+ * @param feed
+ * @returns All items from the feed
+ */
+
+async function getAllItemsFromFeed<T>(feed: Feed<any, T>): Promise<T[]> {
+  let items = [];
+  do {
+    items = items.concat(await feed.items());
+  } while (feed.isMoreAvailable());
+  return items;
+}