fix: Remove problematic .helmignore patterns causing Helm lint failure

The *.md / !README.md pattern combination triggers a bug in Helm v3.17.1
where Chart.yaml is incorrectly excluded, causing "Chart.yaml file is missing"
errors during helm lint.

Author: mattmattox

helm/node-doctor/.helmignore

@@ -24,10 +24,6 @@
 *.tmproj
 .vscode/
 
-# Documentation
-*.md
-!README.md
-
 # Test files
 *_test.yaml
 test/