docs: improve datasource readme (#23653)

lib/modules/datasource/readme.md

@@ -7,7 +7,8 @@ Datasources are used in Renovate primarily to fetch released versions of package
 New datasources _must_ follow the class-based programming style.
 Use the `java-version` datasource as a reference.
 
-Add the datasource to the API in [`api.ts`](api.ts) so that the new datasource is usable. If you find `Pending mocks!` errors in the Jest tests and your mocked URLs are correct, ensure the datasource is correctly registered.
+Add the datasource to the API in [`api.ts`](api.ts) so that the new datasource is usable.
+If you find `Pending mocks!` errors in the Jest tests _and_ your mocked URLs are correct, make sure the datasource is correctly registered.
 
 ## getReleases
 
@@ -16,24 +17,25 @@ The minimum exported interface for a datasource is a function called `getRelease
 The config has:
 
 - `packageName`: the package's full name including scope if present (e.g. `@foo/bar`)
-- `registryUrls`: an array of registry Urls to try
+- `registryUrls`: an array of registry URLs to try
 
 `getReleases` should return an object having:
 
-- `releases`: an array of strings of matched versions. This is the only mandatory field.
+- `releases`: an array of strings of matched versions. This is the only mandatory field
 - `deprecationMessage`: a string description of the package's deprecation notice, if applicable
-- `sourceUrl`: a HTTP URL pointing to the source code (e.g. on GitHub)
-- `homepage`: a HTTP URL for the package's homepage. Ideally should be empty if the homepage and sourceUrl are the same
-- `changelogUrl`: a URL pointing to the package's Changelog (could be a Markdown file, for example). If not present then Renovate will search the `sourceUrl` for a changelog file.
-- `tags`: an object mapping tag -> version, e.g. `tags: { latest: '3.0.0' }`. This is only used by the `followTags` function.
+- `sourceUrl`: a HTTP URL pointing to the source code (for example on GitHub)
+- `homepage`: a HTTP URL for the package's homepage. Ideally should be empty if the homepage and `sourceUrl` are the same
+- `changelogUrl`: a URL pointing to the package's changelog (could be a Markdown file, for example). If not present then Renovate will search the `sourceUrl` for a changelog file
+- `tags`: an object mapping tag -> version, for example `tags: { latest: '3.0.0' }`. This is only used by the `followTags` function
 
 ## getDigest
 
-Datasources that support the concept of digests (e.g. Docker digests and Git commit hashes) also can export a `getDigest` function.
+Datasources that support digests (like Docker digests and Git commit hashes) can export a `getDigest` function.
 
 The `getDigest` function has two inputs:
 
 - `config`: the Renovate config for the package being updated, has the same fields as `getReleases`
 - `newValue`: the version or value to retrieve the digest for
 
-The `getDigest` function returns a string output representing the digest value. If none is found then a return value of `null` should be returned.
+The `getDigest` function returns a string output representing the digest value.
+If no digest is found, the `getDigest` function should return `null`.