Add .git-blame-ignore-revs and prettier instructions (#585)

.git-blame-ignore-revs

@@ -0,0 +1 @@
+193434461dbd9c48fe5dcbad95693470aec422ac

README.md

@@ -16,3 +16,23 @@ Common code referenced across Bitwarden JavaScript projects.
 - _Microsoft Build Tools 2015_ in Visual Studio Installer
 - [Windows 10 SDK 17134](https://developer.microsoft.com/en-us/windows/downloads/sdk-archive/)
   either by downloading it seperately or through the Visual Studio Installer.
+
+## Prettier
+
+We recently migrated to using Prettier as code formatter. All previous branches will need to updated to avoid large merge conflicts using the following steps:
+
+1. Check out your local Branch
+2. Run `git merge 8b2dfc6cdcb8ff5b604364c2ea6d343473aee7cd`
+3. Resolve any merge conflicts, commit.
+4. Run `npm prettier`
+5. Commit
+6. Run `git merge -Xours 193434461dbd9c48fe5dcbad95693470aec422ac`
+7. Push
+
+### Git diff
+
+We also recommend that you configure git to ignore the prettier revision using:
+
+```bash
+git config blame.ignoreRevsFile .git-blame-ignore-revs
+```