docs: multiline pattern issue in windows vs linux (#1678) (#1685)

* closes #1678

cve_bin_tool/checkers/README.md

@@ -59,6 +59,19 @@ A few ways to do it:
   or similar) you can grep for that and then look at the history to see what valid patterns
   look like.
 
+### Multi-line version patterns
+
+In Windows, a new line is denoted using "\r\n" and in Linux it's "\n".
+
+For example, if the version string looks like this:
+
+```
+  <artifactId>commons-compress</artifactId>
+  <version>1.16.1</version>
+```
+
+Then a good regex signature for this will be `r"<artifactId>commons-compress</artifactId>\r?\n  <version>([0-9]+\.[0-9]+(\.[0-9]+)?)</version>"`. And in case of the mapping tests, the `version_strings` parameter doesn't support regex strings, so just use "\r\n" to indicate a new line.
+
 ### Avoiding false positives (beware the X.X.X version pattern!)
 
 It can be very tempting to have a version pattern that matches `X.X.X` where `X` is a number