lintcheck: explain sources.toml configuration

Author: matthiaskrgr

clippy_dev/README.md

@@ -26,3 +26,26 @@ where `custom.toml` must be a relative path from the repo root.
 
 The results will then be saved to `lintcheck-logs/custom_logs.toml`.
 
+### configuring the crate sources
+The sources to check are saved in a `toml` file.  
+There are three types of sources.  
+A crates-io source:
+````toml
+bitflags = {name = "bitflags", versions = ['1.2.1']}
+````
+Requires a "name" and one or multiple "versions" to be checked.
+
+A git source:
+````toml
+puffin = {name = "puffin", git_url = "https://github.com/EmbarkStudios/puffin", git_hash = "02dd4a3"}
+````
+Requires a name, the url to the repo and unique identifier of a commit,
+branch or tag which is checked out before linting.  
+There is no way to always check `HEAD` because that would lead to changing lint-results as the repo would get updated.  
+If `git_url` or `git_hash` is missing, an error will be thrown.
+
+A local dependency:
+````toml
+ clippy = {name = "clippy", path = "/home/user/clippy"}
+````
+For when you want to add a repository that is not published yet.