docs: add ngx-json-treeview (#1300)

Author: jdegand

README.md

@@ -1997,6 +1997,7 @@ for the creation of web applications developed with Angular.
 * [ngx-imageviewer](https://github.com/viobui/ngx-imageviewer) - Generate a image/pdf viewer using canvas.
 * [ngx-json-schema-viewer](https://github.com/jy95/ngx-json-schema-viewer) - JSON Schema Viewer in Angular.
 * [ngx-gist](https://github.com/ProAngular/ngx-gist) - An Angular Material and highlightjs styled display box for GitHub gist and local code snippets.
+* [ngx-json-treeview](https://github.com/MichaelDoyle/ngx-json-treeview) - A collapsible JSON tree view for Angular.
 
 #### Misc Components