Update README.md: increase mockup screenshot sizes, add about osmd screenshot title (#953)

README.md

@@ -26,7 +26,7 @@
 
 ## About OSMD
 
-<img width="500" src="https://user-images.githubusercontent.com/33069673/106186552-bd191300-61a4-11eb-8814-07019fcf1d5b.png">
+<img title="How OSMD can look in the browser&#xA;(Mockup, OSMD on its own does not support playback)" height="350" src="https://user-images.githubusercontent.com/33069673/106186552-bd191300-61a4-11eb-8814-07019fcf1d5b.png">
 
 OpenSheetMusicDisplay renders MusicXML sheet music in the browser. It is the missing link between [MusicXML](https://www.musicxml.com/) and [VexFlow](https://www.vexflow.com/). Built upon many years of experience in both sheet music interactivity and engraving, it is the perfect solution for app developers seeking to build digital sheet music services.
 
@@ -42,7 +42,7 @@ Try the [Public Demo](https://opensheetmusicdisplay.github.io/demo/) to see what
 
 Developers can also run a [local development demo (see Wiki)](https://github.com/opensheetmusicdisplay/opensheetmusicdisplay/wiki/Debugging-(VSCode)):
 
-<img height="300" alt="Local OSMD Developer Demo" src="https://user-images.githubusercontent.com/33069673/106189263-5695f400-61a8-11eb-901f-aafc853af497.png">
+<img height="350" alt="Local OSMD Developer Demo" src="https://user-images.githubusercontent.com/33069673/106189263-5695f400-61a8-11eb-901f-aafc853af497.png">
 
 
 ## Key Features
@@ -55,7 +55,7 @@ Developers can also run a [local development demo (see Wiki)](https://github.com
 * Outputs SVG or PNG, also via nodejs script in the command line, completely browserless (e.g. for server-side rendering)
 * Written in [Typescript](https://www.typescriptlang.org/) with complete type information, 100% compatible with Javascript (minified build is .js)
 
-<img title="OSMD in the Browser" src="https://user-images.githubusercontent.com/33069673/106321958-64fe1180-6275-11eb-8632-3b22beaa0829.jpg" height="200"> <img title="OSMD on Mobile (or server-side rendering)" src="https://user-images.githubusercontent.com/33069673/106321963-67606b80-6275-11eb-8fdd-2acf273586df.jpg" height="200">
+<img title="OSMD in the Browser" src="https://user-images.githubusercontent.com/33069673/106321958-64fe1180-6275-11eb-8632-3b22beaa0829.jpg" height="300"> <img title="OSMD on Mobile (or server-side rendering)" src="https://user-images.githubusercontent.com/33069673/106321963-67606b80-6275-11eb-8fdd-2acf273586df.jpg" height="300">
 
 ## Limitations