docs: add crda remote matcher details

Signed-off-by: Rafiu Jaman Mollah <rmollah@redhat.com>

Documentation/concepts/matching.md

@@ -8,6 +8,17 @@ The matcher API is designed to be called often and will always provide the most
 
 See our [api](../howto/api.md) guide to learn how to view our api specification and work with the Matcher api.
 
+# Remote Matching
+
+A remote matcher behaves similarly to a matcher, except that it uses api calls to fetch vulnerability data for a provided IndexReport.
+Remote matchers are useful when it is not possible to persist data from a given source into the database.
+
+The `crda` remote matcher is responsible for fetching vulnerabilities from Red Hat Code Ready Dependency Analytics (CRDA).
+By default, this matcher serves 100 requests per minute.
+The rate-limiting can be lifted by requesting a dedicated API key, which is done via [this form][CRDA-Request-Form].
+
+[CRDA-Request-Form]: https://docs.google.com/forms/d/e/1FAIpQLSfJ1aoOfi0tQ6_o0srEbYL-cSwzo_MyDJQnwcFG9IYVlNXJrA/viewform?usp=sf_link
+
 ## Summary
 
 In summary you should understand that a Matcher node provides vulnerability reports given the output of an Indexing process. By default it will also run background Updaters keeping the vulnerability database up-to-date.