docs: Process for adding to dict

CONTRIBUTING.md

@@ -27,6 +27,31 @@ Already have an idea?  It might be good to first [create an issue][new issue]
 to propose it so we can make sure we are aligned and lower the risk of having
 to re-work some of it and the discouragement that goes along with that.
 
+### Adding typos
+
+1. Add your type to our data file `crates/typos-dict/assets/words.csv`
+
+Format: `typo,correction[,correction...]`
+
+2. Verify your change
+
+Run
+```bash
+cargo run --package typos-dict-verify -- --input crates/typos-dict/assets/words.csv --output crates/typos-dict/assets/words.csv
+```
+Auto-cleans up your change according to some rules we have like:
+- Don't prefer specific dialects in the dictionary, leaving those to [`varcon`](http://wordlist.aspell.net/varcon-readme/).
+- Mixing up corrections and typos
+- etc
+
+3. Code-gen the dictionary
+
+Run
+```bash
+cargo run --package typos-dict-codegen -- --output crates/typos-dict/src/dict_codegen.rs
+```
+(we do development-time code-gen to speed up builds)
+
 ### Process
 
 When you first post a PR, we request that the commit history get cleaned