docs: replace Slack to Discord (#5514)

Author: janoshrubos

README.md

@@ -344,7 +344,7 @@ To use the locally built CLI instead `tns` you can call `PATH_TO_CLI_FOLDER/bin/
 Get Help
 ===
 
-Please, use [github issues](https://github.com/NativeScript/nativescript-cli/issues) strictly for [reporting bugs](CONTRIBUTING.md#report-an-issue) or [requesting features](CONTRIBUTING.md#request-a-feature). For general NativeScript questions and support, check out [Stack Overflow](https://stackoverflow.com/questions/tagged/nativescript) or ask our experts in the [NativeScript community Slack channel](https://www.nativescript.org/slack-invitation-form).
+Please, use [github issues](https://github.com/NativeScript/nativescript-cli/issues) strictly for [reporting bugs](CONTRIBUTING.md#report-an-issue) or [requesting features](CONTRIBUTING.md#request-a-feature). For general NativeScript questions and support, check out [Stack Overflow](https://stackoverflow.com/questions/tagged/nativescript) or ask our experts in the [NativeScript community Discord channel](https://nativescript.org/discord).
 
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lib/commands/post-install.ts

@@ -68,7 +68,7 @@ export class PostInstallCliCommand implements ICommand {
 
 		this.$logger.info("");
 		this.$logger.printMarkdown(
-			"If you have any questions, check Stack Overflow: `https://stackoverflow.com/questions/tagged/nativescript` and our public Slack channel: `https://nativescriptcommunity.slack.com/`"
+			"If you have any questions, check Stack Overflow: `https://stackoverflow.com/questions/tagged/nativescript` and our public Discord channel: `https://nativescript.org/discord`"
 		);
 	}
 }

lib/services/platform-environment-requirements.ts

@@ -178,7 +178,7 @@ export class PlatformEnvironmentRequirements
 				platform ? `build for ${platform}` : "build"
 			}, verify that your environment is configured according to the system requirements described at ${
 				this.$staticConfig.SYS_REQUIREMENTS_LINK
-			}. If you have any questions, check Stack Overflow: 'https://stackoverflow.com/questions/tagged/nativescript' and our public Slack channel: 'https://nativescriptcommunity.slack.com/'`
+			}. If you have any questions, check Stack Overflow: 'https://stackoverflow.com/questions/tagged/nativescript' and our public Discord channel: 'https://nativescript.org/discord/'`
 		);
 	}