Remove hardcoded width on the pictures displayed by markdown files. (#2095)

Update etc/images/Primary_logo_blue.png to have the natural width be 600px

HELIDON-CLI.md

@@ -45,5 +45,5 @@ restart your application.
 ## Demo
 
 <p align="center">
-    <img src="etc/images/Helidon_cli.gif" height="572">
+    <img src="etc/images/Helidon_cli.gif">
 </p>

README.md

@@ -1,5 +1,5 @@
 <p align="center">
-    <img src="./etc/images/Primary_logo_blue.png" height="180">
+    <img src="./etc/images/Primary_logo_blue.png">
 </p>
 <p align="center">
     <a href="https://github.com/oracle/helidon/tags">
@@ -105,7 +105,7 @@ but a couple are handy to use on your desktop to verify your changes.
 
 * See the [Helidon FAQ](https://github.com/oracle/helidon/wiki/FAQ)
 * Ask questions on Stack Overflow using the [helidon tag](https://stackoverflow.com/tags/helidon)
-* Join us on Slack: [#helidon-users](https://join.slack.com/t/helidon/shared_invite/enQtNDM1NjU3MjkyNDg2LWNiNGIzOGFhZDdjNzAyM2Y2MzlmMDI4NWY4YjE1OWQ2OTdkYTZkN2FlNDcxNmUyZmZmMTZhZmZhNWI2ZTI1NGI)
+* Join us on Slack: [#helidon-users](http://slack.helidon.io)
 
 ## Get Involved