Added docs to build.rs.

build.rs

@@ -1,15 +1,23 @@
 use std::fs;
 use std::path::Path;
 
+/// If no `.env` file exists, this function will create an `.env` file and copy the contents
+/// of `sample.env` into it (this is why `sample.env` is kept under source control).
+///
+///
+/// # Panics
+///
+/// This function panics if both the `.env` file and `sample.env` file do not exist, or if we
+/// fail to copy `sample.env` into `.env`.
 fn create_env_file_if_dne() {
     let env_path = Path::new(".env");
     if !env_path.exists() {
         let sample_env_path = Path::new("sample.env");
         if !sample_env_path.exists() {
-            panic!("neither the .env nor the sample.env files exist");
+            panic!("neither the `.env` nor the `sample.env` files exist, one of these files must exist to build the `poagov`");
         }
         fs::copy(sample_env_path, env_path)
-            .unwrap_or_else(|e| panic!("could not create .env file from sample.env: {:?}", e));
+            .unwrap_or_else(|e| panic!("failed to create the `.env` file from `sample.env`: {:?}", e));
     }
 }