Fix broken links to the correct page (#1727)

apm-dist/release-docs/README.txt

@@ -20,10 +20,10 @@ Getting Started
 To help you get started, try the following links:
 
 Getting Started
-    https://github.com/apache/incubator-skywalking/blob/master/docs/en/Quick-start.md
+    https://github.com/apache/incubator-skywalking/blob/5.x/docs/en/Quick-start.md
 
 Building
-    https://github.com/apache/incubator-skywalking/blob/master/docs/en/How-to-build.md
+    https://github.com/apache/incubator-skywalking/blob/5.x/docs/en/How-to-build.md
 
 We welcome contributions of all kinds, for details of how you can help
     https://github.com/apache/incubator-skywalking/blob/master/CONTRIBUTING.md
@@ -32,7 +32,7 @@ Find the issue tracker from here
     https://github.com/apache/incubator-skywalking/issues
 
 Find our roadmap
-    https://github.com/apache/incubator-skywalking/blob/master/docs/ROADMAP.md
+    https://github.com/apache/incubator-skywalking/blob/5.x/docs/ROADMAP.md
 
 
 Please help us make Apache SkyWalking better - we appreciate any feedback
@@ -46,4 +46,4 @@ Licensing
 ===============================================================================
 
 This software is licensed under the terms you may find in the file
-named "LICENSE" in this directory.
\ No newline at end of file
+named "LICENSE" in this directory.