Start of new Git Intermediate lessons

This Introduction borrows heavily from characters, concepts, and prose
from git/beginner/00-intro.md by @gvwilson.

git/intermediate/00-intro.md

@@ -0,0 +1,67 @@
+---
+layout: lesson
+root: ../..
+title: Introducing Version Control
+level: intermediate
+---
+Barbara Biologist and Candace Cosmologist have been hired by Universal Missions
+(a space services spinoff from Euphoric State University)
+to figure out where the company should send its next planetary lander.
+Since their couple biocosmology simulation software is still being developed,
+they need to coordinate the changes between
+Barbara's biology code and Candace's new cosmology simulations.
+Barbara and Candace are developing more than just a report;
+their reproducible analysis will include data, code, figures, and text.
+New online writing collaboration tools
+such as writeLaTeX , Google Docs, and Microsoft SkyDrive
+can support their distributed authoring process,
+but so far they've relied on email and Dropbox
+to coordinate the rest of their development.
+
+Although they want to be able to work on the report at the same time,
+they have run into problems doing this in the past.
+If they take turns,
+each one will spend a lot of time waiting for the other to finish,
+but if they work on their own copies and email changes back and forth,
+things will be lost, overwritten, or duplicated.
+Barbara and Candace also fear
+this process of communicating changes
+to code, data, figures, and text
+won't scale as they add more scientists to their team.
+A final concern,
+is that the text and graphics in their report,
+might fall out of sync with the code that generated them,
+and that they might accidentally publish a chart,
+their code can't reproduce
+and that they can no longer explain.
+
+Barbara and Candace decide to use [ADDTHISDESCRIPTION][distributed version control](../gloss.html#version-control)
+to manage their workflow.
+Distributed version control is better than mailing files back and forth or cloud-based syncing services because:
+
+*   Nothing that is committed to version control is ever lost.
+    This means it can be used like the "undo" feature in an editor,
+    and since all old versions of files are saved
+    it's always possible to go back in time to see exactly who wrote what on a particular day,
+    or what version of a program was used to generate a particular set of results.
+*   It keeps a record of who made what changes when,
+    so that if people have questions later on,
+    they know who to ask.
+*   It's hard (but not impossible) to accidentally overlook or overwrite someone's changes,
+    because the version control system highlights them automatically.
+*   Authors can checkpoint their work, even when they're not connected to the Internet.
+    This means that Barbara can experimentally try out new predator-prey models
+    without worrying about changing the main simulation,
+    and that Candace can checkpoint her work on the report at any time,
+    even when her cable provider's Internet connection,
+    mysteriously fails in the middle of the day.
+
+This lesson shows how to use
+a popular open source distributed version control system called Git.
+It is more complex than some alternatives,
+but it is widely used,
+and is further augmented by a free hosting site called [GitHub](http://github.com).
+No matter which distributed version control system you use,
+the most important thing to learn is not the details of their more obscure commands,
+but the fundamentals of how they work,
+and the workflow that they encourage.