README: add function/operator table

Author: stsnel

Diff for: README.md

@@ -31,3 +31,16 @@ version of coverage measurement software.
 The string extractor has a cache, which is enabled by default and can
 optionally be persisted to a file. This helps with efficiently handling loops
 in code, as well as overlapping execution traces.
+
+## Overview of recognized functions and operators
+
+|Node type | Function or operator | Type of constant extracted | Example expression|
+|----------|----------------------|----------------------------| ------------------|
+|Comparison | == (equals operator) | Full string | a == "foo" |
+|Comparison | != (does not equal operator) | Full string | a != "foo" |
+|Comparison | in (part of operator) | String fragment | "foo" in a |
+|Comparison | in (match with collection) | List of full strings | a in ["foo","bar"] |
+|Call | string.startswith | String prefix | a.startswith("foo") |
+|Call | string.endswith | String suffix | a.endswith("foo") |
+|Call | string.find | String fragment | a.find("foo") |
+|Call | string.index | String fragment | a.index("foo") |