docs: Adding the beginning of a migration guide

Currently just a list of notes about required/breaking changes in the repo that MFEs will need to address when migrating.

README.md

@@ -97,3 +97,10 @@ Replace the import from 'frontend-build' with 'frontend-base'.
 ### 8. Search for any other usages of `frontend-build`
 
 Find any other imports/usages of `frontend-build` in your repository and replace them with `frontend-base` so they don't break.
+
+## Migrating to frontend-base
+
+Currently this section is a quick of notes documenting required changes to MFEs.  We will turn this into a more rigorous migration guide in the future.
+
+- First follow the steps above in the "Development" section.
+- Description fields are now required on all i18n messages in the repository.  This is because of a change to the ESLint config.

config/.eslintrc.js

@@ -32,7 +32,7 @@ module.exports = {
     'formatjs/enforce-description': ['error', 'literal'],
     'import/no-import-module-export': 'off',
     'react/function-component-definition': [2, { namedComponents: 'arrow-function' }],
-    "react/jsx-filename-extension": [1, { "extensions": [".tsx", ".jsx"] }]
+    'react/jsx-filename-extension': [1, { extensions: ['.tsx', '.jsx'] }],
   },
   globals: {
     newrelic: false,