Modify setup.py to allow for successful readthedocs installation

Author: rhpvorderman

setup.py

@@ -19,6 +19,7 @@
 # SOFTWARE.
 
 import os
+import sys
 from pathlib import Path
 
 from setuptools import Extension, find_packages, setup
@@ -29,6 +30,10 @@
 CONDA_PREFIX = os.environ.get("CONDA_PREFIX")
 if CONDA_PREFIX:
     EXTENSION_OPTS["include_dirs"] = [os.path.join(CONDA_PREFIX, "include")]
+if os.environ.get("READTHEDOCS"):
+    # Readthedocs uses a conda environment but does not activate it.
+    EXTENSION_OPTS["include_dirs"].append(
+        os.path.join(sys.exec_prefix, "include"))
 
 setup(
     name="isal",