feat: added Index Builder accordions with text descriptions of Custom Index calculations

[bodom0015]

Problem

We would like to add a bit more detail/context surrounding the following:

1. How is the Custom Index calculated from raw numerical values?
2. Why are the numerical weights sometimes different from the percentages supplied?

Fixes #139

Approach

• feat: added an accordion to describe the mathematical and statistical calculations involved in computing the custom index
• feat: added an accordion to differentiate between the numerical weight (on/beside the slider) and the percentage shown on the pie chart

How to Test

1. Navigate to /builder
2. Select 1 or more indicators and click Next
   • You should be navigated to the Choose Weights page
   • You should see the two new text accordions shown here
3. Click the accordion that reads "How are these weights used to calculate the Custom Index?"
   • You should see an explanation of the numerical calculations involved in creating the Custom Index
4. Click the same accordion header again to close the explanation
5. Click on the accordion that reads "Why is there a difference between numerical weight and the percentage applied?"
   • You should see an explanation / example of how the percentages are calculated on the pie chart
6. Click the same accordion header again to close the explanation

[netlify[bot]]

✅ Deploy Preview for chicago-env-explorer ready!

Name	Link
🔨 Latest commit	585734aaee2c7e3d869dfa57fa1499ceceb7c4ce
🔍 Latest deploy log	https://app.netlify.com/sites/chicago-env-explorer/deploys/660ee8e88542790008761086
😎 Deploy Preview	https://deploy-preview-144--chicago-env-explorer.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.