docs(ctb): Document use of OZ as a default when available

packages/contracts-bedrock/README.md

@@ -195,6 +195,11 @@ After the initial Bedrock upgrade, contracts MUST use the following versioning s
 
 We have made an exception to the `Semver` rule for the `WETH` contract to avoid making changes to a well-known, simple, and recognizable contract.
 
+### Dependencies
+
+Where basic functionality is already supported by an existing contract in the OpenZeppelin library,
+we should default to using the Upgradeable version of that contract.
+
 ### Tests
 
 Tests are written using Foundry.
@@ -207,7 +212,7 @@ These guidelines are also encoded in a script which can be run with:
 ts-node scripts/forge-test-names.ts
 ```
 
-*Note: This is a work in progress, not all test files are compliant with these guidelines.*
+_Note: This is a work in progress, not all test files are compliant with these guidelines._
 
 #### Organizing Principles