Also check .txt files with rstcheck (#2384)

* Also check .txt files with rstcheck.

* Ignore .txt files in docs/docsite/rst/getting_started/ansible_output.

Author: felixfontein

tests/checkers/rstcheck.json

@@ -1,8 +1,10 @@
 {
     "extensions": [
-        ".rst"
+        ".rst",
+        ".txt"
     ],
     "ignore_regexs": [
-        "^docs/docsite/rst/porting_guides/porting_guide_[0-9]+\\.rst$"
+        "^docs/docsite/rst/porting_guides/porting_guide_[0-9]+\\.rst$",
+        "^docs/docsite/rst/getting_started/ansible_output/.*\\.txt$"
     ]
 }