Let's start with some definitions
A Customer Journey Map should reflect what the CURRENT journey feels like.
Your requirements document should reflect what the ideal version of their journey SHOULD feel like.
Notice I used the word "Feel" because what you're creating is technically an empathic map of the customer's journey.
Add in Customer Statements
A key item to include is actual feedback from your users. When mapping the Customer Journey, add in actual comments from users regarding their frustrations, enjoyments, and any other emotions at any point on the journey. You will eventually start getting a bigger picture of what's happening and where your solution can fit in to make their journey easier or more efficient.
Here is a picture to help make this less vague:

In this example, they've included some archetypes, mapped out the current journey, the customer's high points and low points, and opportunities/barriers.
It's important to note that the purpose of this artifact is to gain insights in order to innovate the process.
Turn all negatives into positives, Turn all positives into joy
Take the feedback and turn that into a list of needs based on any insights from your map. If there are any pain-points, try to turn that around by brainstorming a solution for that. If there are any positive-points, try to see if you can make it easier, or incorporate that into your new tool.
Are there any items that take extra time in the current process? Is this intentional?
How do you simplify this process? Can some steps be combined?
Are more steps needed to reduce cognitive load at each part?
From this you can get a pretty decent picture of what is necessary in order to disseminate into your requirements listing.
Here's an overly simplified Example
Customer wants to buy a Scarf.
Based on some fictitious research, we find the journey to look like this:
The person goes to the store. They get lost and feel frustrated trying to find the right aisle. When they do find the aisle, they are bombarded with all the tangled mess of cloths tassles and various colours. They like that there is great selection but feel overwhelmed by all the choices. In the end, they leave because they can't find what they are looking for and does not wish to spend more time searching. They leave.
What are the pain points?
- Inability to navigate the store
- Lack of organization of product
- Spent too much time on the Hunt
- No one was around to provide assistance
What are positives?
- Excellent selection of product
Map the feedback into a solution.
The ideal journey should look like this:
Customer goes the store. They easily find what where the product they need is. The product is organized and displayed in a way that makes it easy for him/her to explore what they want. They pick 2 scarves and buy. In and out. It was so easy they would go back and also recommend your store.
You can already see the requirements list that is developing.
How does the customer find where the product is easily? Perhaps with some clear signage or a map.
How does the customer discover the scarf they want? Perhaps some are on a manikin and it's all organized on a rack or folded neatly on a table. They are able to feel the texture of each scarf and visualize the look.
As an added bonus, the store has helpful staff to point the way and provide assistance as needed to personalize the journey.
Makes sense?
The process was laid out much better in this article by Desonance:
http://desonance.wordpress.com/2010/06/16/customer-experience-mapping/
Here are some great examples of Maps:
http://www.joycehostyn.com/blog/2010/03/22/visualizing-the-customer-experience-using-customer-experience-journey-maps/
Hope this helps.