policy updates

README.md

@@ -80,11 +80,33 @@ Here are some style notes for the `dat` files:
 
  1. Record debits first.
 
- 1. Symmetry is nice. 
+ 1. Symmetry is nice.
+
+ 1. Explicate all transaction amounts (don't depend on ledger's implicit
+    transaction balancing).
 
  1. Use comments! Especially for weird stuff.
 
 
+### Change Restrictions
+
+We start a PR for each month, named `YYYY-MM`, and we close the month by
+merging the PR.
+
+Inside of an open month, we should overwrite ledger transactions as needed.
+Changes are tracked in git commits and GitHub comments.
+
+Outside of an open month, we must make correcting transactions in the current
+month, rather than overwriting transactions in the old dat file.
+
+Inside of an open year, we may change account names (this affects all month
+files for the year).
+
+Outside of an open year, we must archive accounts rather than renaming them.
+
+It's always okay to add comments to a file.
+
+
 ### Access
 
 Many accounting tasks require access to Gratipay's bank and payment processor