Inline comments in .travis.yml for CACHIX_CACHE/NUR_REPO

During setup, I wondered what the format of this variables is. While
searching for sample values, I noticed that people use these
inconsistently. So better be explicit.

I removed the paragraph from the README.md to avoid duplication.

.travis.yml

@@ -4,7 +4,20 @@ sudo: false
 
 env:
   global:
+    # Set this to cache your build results in cachix for faster builds
+    # in travis and for everyone who uses your cache.
+    #
+    # Format: Your cachix cache host name without the ".cachix.org" suffix.
+    # Example: mycache (for mycache.cachix.org)
+    #
+    # For this to work, you also need to set the  CACHIX_SIGNING_KEY
+    # in your repository settings in Travis.
     - CACHIX_CACHE=
+    # Set this to notify the global nur package registry that changes are
+    # available.
+    #
+    # The repo name as used in
+    # https://github.com/nix-community/NUR/blob/master/repos.json
     - NUR_REPO=<YOUR_NUR_REPO_NAME_HERE>
 
 matrix:

README.md

@@ -12,8 +12,6 @@
    * Library functions, modules and overlays go in the respective directories
 3. Add your NUR repo name and your cachix repo name (optional) to
    [.travis.yml](./.travis.yml)
-   * If you use cachix you should also add your cache's private key to travis'
-     protected env variables
 4. Enable travis for your repo
    * You can add a cron job in the repository settings on travis to keep your
      cachix cache fresh