Doc: Update coding style

readme/coding_style.md

@@ -32,6 +32,26 @@ If this is a large file however please ask first if it needs to be converted. So
 
 In TypeScript files prefer `import` to `require` so that we can benefit from type-checking. If it does not work, you may have to add the type using `yarn add @types/NAME_OF_PACKAGE`. If you are trying to import an old package, it may not have TypeScript types and in this case using `require()` is acceptable.
 
+### Avoid inline styles
+
+In general please define types separately as it improves readability and it means the type can be re-used.
+
+**BAD:**
+```ts
+const config: { [key: string]: Knex.Config } = {
+	// ...
+}	
+```
+
+**Good:**
+```ts
+type Config = Record<string, Knex.Config>;
+
+const config: Config = {
+	// ...
+}	
+```
+
 ## Filenames
 
  * `camelCase.ts`: Files that export multiple things.