Explain API versions

Adds a brief paragraph about v1.1 and v2.

docs/tutorial.md

@@ -5,7 +5,7 @@ Twarc is a command line tool for collecting Twitter data via Twitter's web Appli
 By the end of this tutorial, you will have:
 
 1. Familiarised yourself with interacting with a command line application via a terminal
-2. Setup twarc so you can collect data from the Twitter API
+2. Setup twarc so you can collect data from the Twitter API (version 2)
 3. Constructed two Twitter search queries to address a specific research question
 4. Collected data for those two queries
 5. Processed the collected data into formats suitable for other analysis
@@ -70,6 +70,9 @@ Here are some examples of things you can do with the Twitter API:
 - Map Twitter account followers and followees within or around a group of users
 - Trace conversations and interactions around users or tweets of interest
 
+You may notice as you read about the Twitter API that there are two versions of the Twitter API - version 1.1 and version 2. At the time of writing,
+Twitter is providing both versions of the API, but at some unknown point in the future version 1.1 may be discontinued. Twarc can handle either API version: the `twarc` command uses version 1.1 of the Twitter API, the `twarc2` command uses version 2. Take care when reading documentation and tutorials as to which Twitter API version is being referenced. This tutorial uses version 2 of the Twitter API.
+
 Twitter API endpoints can be structured either around tweets or around user accounts. For example, the search endpoint provides lists of tweets - user information is included, but the data is focused on the tweets.
 
 The available endpoints and their details are evolving as Twitter develops and releases its API v2, for the most up to date information refer to [the Twitter API documentation](https://developer.twitter.com/en/docs/twitter-api). Some of the most used endpoints for research purposes are: