README.md: Add "NI created and supports this package" and fix .gitattributes (#22)

- [x] This contribution adheres to
[CONTRIBUTING.md](https://github.com/ni/nisync-python/blob/main/CONTRIBUTING.md).

### What does this Pull Request accomplish?

Add "NI created and supports this package" to README.md.

Fix the `*.png` wildcard in `.gitattributes` so Git doesn't treat all
files as binary.

### Why should this Pull Request be merged?

Clarify that this is the official NI-Sync API package from NI.

### What testing has been done?

N/A

---------

Signed-off-by: Brad Keryan <[email protected]>
Signed-off-by: Wai Kin Chung <[email protected]>
Co-authored-by: Wai Kin Chung <[email protected]>

Author: bkeryan

.gitattributes

@@ -1,2 +1,2 @@
-* text eol=lf
-* png binary
+* text eol=lf
+* .png binary

README.md

@@ -20,6 +20,7 @@
 
 The **nisync** package allows you to develop timing and synchronization applications 
 for both time-based and signal-based synchronizations with NI-Sync devices in Python.
+NI created and supports this package.
 
 ## Documentation