Update README

Author: ongardie

README.md

@@ -3,17 +3,31 @@ The Raft Consensus Algorithm
 
 This is the repo for Raft website: https://raft.github.io
 
-Please contribute to the website by submitting pull requests or creating
-issues.
+Please contribute to the website by submitting pull requests (preferably) or
+creating issues. The most common way people contribute is by adding a new
+implementation to `implementations.json`. Note that the file is ordered
+lexicographically by GitHub repo URL, and this is strictly enforced by automated
+checks.
 
-The website is hosted as a GitHub static page. To run it locally, start a local
-static webserver:
+When you submit a PR, `./check.py` will make sure the data is well-formed. If
+you want to run it locally, you'll need the
+[`jsonschema`](https://pypi.org/project/jsonschema/) library first:
+```
+pip3 install jsonschema
+```
+
+The website is hosted as a GitHub static page at <https://raft.github.io>. To
+run it locally, start a local static webserver:
 ```
 python3 -m http.server 8000 --bind localhost
 ```
 and open <http://localhost:8080/>. The server is needed to allow `index.html` to
 pull down `implementations.json`.
 
+The implementations are sorted on the website according to GitHub stars and last
+update time. This information is cached on a separate server a few times a day,
+so new implementations will initially appear at the bottom of the table for a
+few hours.
 
 This work is licensed under a Creative Commons Attribution 3.0 Unported License.
 See http://creativecommons.org/licenses/by/3.0/deed.en_US for details.