Replace README link with absolute link so it will work when uploaded to PyPI

Also:
- Fix casing of color when calling "set foreground color" in getting_started.md

Author: tleonhardt

README.md

@@ -75,7 +75,7 @@ Hello, Ada!
 Hello, Ada!
 ```
 
-[![Animated demonstration of the cmd2 quick-start application](docs/assets/cmd2-readme-demo.gif)](docs/assets/cmd2-readme-demo.gif)
+[![Animated demonstration of the cmd2 quick-start application](https://raw.githubusercontent.com/python-cmd2/cmd2/main/docs/assets/cmd2-readme-demo.gif)](https://raw.githubusercontent.com/python-cmd2/cmd2/main/docs/assets/cmd2-readme-demo.gif)
 
 See the [getting started tutorial](https://cmd2.readthedocs.io/en/latest/examples/getting_started/)
 to build a more complete application.

docs/examples/getting_started.md

@@ -93,7 +93,7 @@ against `fg_colors`. Use the built-in `set` command to inspect or change it:
 
 ```shell
 myapp> set foreground_color
-myapp> set foreground_color Red
+myapp> set foreground_color red
 ```
 
 The first command displays the current value. The second changes the color used by subsequent `echo`