Update README.md (#39)

# *Name of the PR*
Update text in the Example description

## ♻️ Current situation & Problem
The Example in the READMe file provides an example on how to convert
HealthKit heart rate samples into FHIR observations. The text originally
stated "step count data". The description was updated to replace "step
count" with "heart rate".

### Code of Conduct & Contributing Guidelines 

By submitting creating this pull request, you agree to follow our [Code
of
Conduct](https://github.com/StanfordBDHG/.github/blob/main/CODE_OF_CONDUCT.md)
and [Contributing
Guidelines](https://github.com/StanfordBDHG/.github/blob/main/CONTRIBUTING.md):
- [x] I agree to follow the [Code of
Conduct](https://github.com/StanfordBDHG/.github/blob/main/CODE_OF_CONDUCT.md)
and [Contributing
Guidelines](https://github.com/StanfordBDHG/.github/blob/main/CONTRIBUTING.md).

Co-authored-by: Paul Schmiedmayer <PSchmiedmayer@users.noreply.github.com>

README.md

@@ -73,7 +73,7 @@ let allergyIntolerance = try allergyRecord.resource.get(if: AllergyIntolerance.s
 
 ## Example
 
-In the following example, we will query the HealthKit store for step count data, convert the resulting samples to FHIR observations, and encode them into JSON.
+In the following example, we will query the HealthKit store for heart rate data, convert the resulting samples to FHIR observations, and encode them into JSON.
 
 ```swift
 import HealthKitOnFHIR