Add some usage documentation to the block traffic module

Author: carols10cents

src/config.rs

@@ -43,6 +43,8 @@ impl Default for Config {
     /// - `GH_CLIENT_ID`: The client ID of the associated GitHub application.
     /// - `GH_CLIENT_SECRET`: The client secret of the associated GitHub application.
     /// - `DATABASE_URL`: The URL of the postgres database to use.
+    /// - `BLOCKED_TRAFFIC`: A list of headers and environment variables to use for blocking
+    ///.  traffic. See the `block_traffic` module for more documentation.
     fn default() -> Config {
         let checkout = PathBuf::from(env("GIT_REPO_CHECKOUT"));
         let api_protocol = String::from("https");

src/middleware/block_traffic.rs

@@ -1,4 +1,11 @@
 //! Middleware that blocks requests if a header matches the given list
+//! To use, set the `BLOCKED_TRAFFIC` environment variable to a comma-separated list of pairs
+//! containing a header name, an equals sign, and the name of another environment variable that
+//! contains the values of that header that should be blocked. For example, set `BLOCKED_TRAFFIC`
+//! to `User-Agent=BLOCKED_UAS,X-Real-Ip=BLOCKED_IPS`, `BLOCKED_UAS` to `curl/7.54.0,cargo 1.36.0
+//! (c4fcfb725 2019-05-15)`, and `BLOCKED_IPS` to `192.168.0.1,127.0.0.1` to block requests from
+//! the versions of curl or Cargo specified or from either of the IPs (values are nonsensical
+//! examples). Values of the headers must match exactly.
 
 use super::prelude::*;