docs: document mfs write content argument

Author: achingbrain

SPEC/FILES.md

@@ -771,7 +771,7 @@ ipfs.files.readReadableStream('/hello-world', (err, stream) => {
 
 ##### `Go` **WIP**
 
-##### `JavaScript` - ipfs.files.readReadableStream(path, [options], [callback])
+##### `JavaScript` - ipfs.files.readPullStream(path, [options], [callback])
 
 Where:
 
@@ -810,8 +810,11 @@ Where:
 
 - `path` is the path of the object to write.
 - `content` can be:
-  - a Buffer instance.
-  - a Path (caveat: will only work in Node.js).
+  - a [`Buffer`][b]
+  - a [`PullStream`][ps]
+  - a [`ReadableStream`][rs]
+  - a [`Blob`][blob] (caveat: will only work in the browser)
+  - a string path to a file (caveat: will only work in Node.js)
 - `options` is an optional Object that might contain the following keys:
   - `offset` is an Integer with the byte offset to begin writing at.
   - `create` is a Boolean to indicate to create the file if it doesn't exist.
@@ -924,3 +927,4 @@ ipfs.files.ls('/screenshots', function (err, files) {
 [rs]: https://www.npmjs.com/package/readable-stream
 [ps]: https://www.npmjs.com/package/pull-stream
 [cid]: https://www.npmjs.com/package/cids
+[blob]: https://developer.mozilla.org/en-US/docs/Web/API/Blob