Require torch in requirements.txt

Author: elcorto

requirements.txt

@@ -1,5 +1,12 @@
-# See install/README.md
-##torch
+# Most install sites will want to use an already installed torch or install a
+# specific version before installing mala, e.g. via
+#
+#   pip install --extra-index-url https://download.pytorch.org/whl/cu<cuda_version> torch==<torch_version>
+#
+# The requirement below makes sure we have torch installed, even if that will
+# pull the latest GPU torch in case the user's environment may be misconfigured
+# such that a pre-installed torch is not found.
+torch
 
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