Updates to the API opening text (#561)

Updated the opening text at the top of each of the API pages (Provider, Agency, Policy) using the text on the main readme to give more context for people landing on these pages directly.

Author: schnuerle

agency/README.md

@@ -1,6 +1,8 @@
 # Mobility Data Specification: **Agency**
 
-This specification contains a collection of RESTful APIs used to specify the digital relationship between *mobility as a service* Providers and the Agencies that regulate them.
+The Agency API endpoints are intended to be implemented by regulatory agencies and consumed by mobility providers. Providers query the Agency API when events (such as a trip start or vehicle status change) occur in their systems.
+
+This specification contains a collection of RESTful APIs used to specify the digital relationship between *mobility as a service* providers and the agencies that regulate them.
 
 ## Table of Contents
 

policy/README.md

@@ -1,6 +1,8 @@
 # Mobility Data Specification: Policy
 
-This specification describes the digital relationship between _mobility as a service_ Providers and the Agencies that regulate them. The Policy specification is meant to communicate municipal policies (such as as vehicle deployment caps and speed limits) in a clear, consistent manner.
+The Policy API endpoints are intended to be implemented by regulatory agencies and consumed by mobility providers. Providers query the Policy API to get information about local rules that may affect the operation of their mobility service or which may be used to determine compliance.
+
+This specification describes the digital relationship between _mobility as a service_ providers and the agencies that regulate them. The Policy API communicates municipal policies (such as as vehicle deployment caps and speed limits) in a clear, consistent manner.
 
 ## Table of Contents
 

provider/README.md

@@ -1,5 +1,7 @@
 # Mobility Data Specification: **Provider**
 
+The Provider API endpoints are intended to be implemented by mobility providers and consumed by regulatory agencies. When a municipality queries information from a mobility provider, the Provider API has a historical view of operations in a standard format.
+
 This specification contains a data standard for *mobility as a service* providers to define a RESTful API for municipalities to access on-demand.
 
 ## Table of Contents