Update documentation for MD023/heading-start-left to include "indented" example within block quote (fixes #1009).

doc-build/md023.md

@@ -14,5 +14,12 @@ Some text
 # Heading
 ```
 
+Note that scenarios like block quotes "indent" the start of the line, so the
+following is also correct:
+
+```markdown
+> # Heading in Block Quote
+```
+
 Rationale: Headings that don't start at the beginning of the line will not be
 parsed as headings, and will instead appear as regular text.

doc/Rules.md

@@ -875,6 +875,13 @@ Some text
 # Heading
 ```
 
+Note that scenarios like block quotes "indent" the start of the line, so the
+following is also correct:
+
+```markdown
+> # Heading in Block Quote
+```
+
 Rationale: Headings that don't start at the beginning of the line will not be
 parsed as headings, and will instead appear as regular text.
 

doc/md023.md

@@ -22,5 +22,12 @@ Some text
 # Heading
 ```
 
+Note that scenarios like block quotes "indent" the start of the line, so the
+following is also correct:
+
+```markdown
+> # Heading in Block Quote
+```
+
 Rationale: Headings that don't start at the beginning of the line will not be
 parsed as headings, and will instead appear as regular text.