Add manual linking instructions

There are a million issues around people having issues with automatically linking and having a link to manual instructions would address a lot of these up front. This also follows the instructions pattern of most react native modules.

Response typo

Bug Fix: getExternalFilesDir null check

compatible with RN > 0.49

Fix typo: "Status" instead of "Statu"

Update README with proper status code handling

RN > 0.49 requires to implement requiresMainQueueSetup.
this fix and suppress that yellow box warning

```
Module RNFetchBlob requires main queue setup since it overrides `init` but doesn't implement `requiresMainQueueSetup`. In a future release React Native will default to initializing all native modules on a background thread unless explicitly opted-out of.
```

Synchronized tables, separated requests and network logic and other...

Inform linter that we're handling android api versions correctly

Implement `requiresMainQueueSetup`, fixes #553

Fix README.md

Fix README