Update the desc for `node_dump` in issue templates

Putting the link to [node_dump script](https://github.com/emqx/emqx/blob/master/bin/node_dump)  will lead the user to download the node_dump script directly from the github, and run it.

.github/ISSUE_TEMPLATE/bug-report.md

@@ -2,7 +2,8 @@
 name: Bug Report
 about: Create a report to help us improve
 title: ''
-labels: needs-triage
+labels: ''
+assignees: ''
 
 ---
 
@@ -18,7 +19,7 @@ Describe your issue here.
 
 ### Your environment
 
-For EMQ X 4.3 or newer, please provide the log archive generated by [node_dump tool](https://github.com/emqx/emqx/blob/master/bin/node_dump) 
+For EMQ X 4.3 or newer, please provide the log archive generated by running `node_dump` (The `node_dump` script can be found in `/<path-to-installation-of-emqx>/bin` if you installed emqx from source or zip ball).
 
 - EMQ X version (e.g. `emqx_ctl status`): 
 - Hardware configuration (e.g. `lscpu`):

.github/ISSUE_TEMPLATE/feature-request.md

@@ -2,7 +2,8 @@
 name: Feature Request
 about: Suggest an idea for this project
 title: ''
-labels: "Feature, needs-triage"
+labels: Feature
+assignees: ''
 
 ---
 

.github/ISSUE_TEMPLATE/support-needed.md

@@ -2,7 +2,8 @@
 name: Support Needed
 about: Asking a question about usages, docs or anything you're insterested in
 title: ''
-labels: "Support, needs-triage"
+labels: Support
+assignees: ''
 
 ---