Added verificarlo based compilation info in TODO. #29

TODO.org

@@ -1,3 +1,5 @@
+#+STARTUP: showeverything
+
 * Set up CI on Travis
 * Write tests
 
@@ -19,3 +21,28 @@ context.
 * Put pictures
 * Make the Makefile part of the documented code ?
 * Put the data-flow graph in the code.
+
+* Verificarlo TODO
+These are installation instructions for
+verificarlo which needs to be moved to 
+an appropriate place at some point.
+** Compilation and Testing
+
+The following steps were required to get
+the verificarlo version up and running on
+an Ubuntu 20.04 laptop.
+
+1. Compilers
+   a. clang - For e.g. clang-7
+   b. flang - For e.g. flang-7 : Care needs to be taken
+                                 that the flang version 
+                                 is compatible with the
+                                 clang version used.
+                                 There are known issues
+                                 with using oneAPI due
+                                 to flang being incompatible
+                                 with oneAPI supplied clang.
+   c. gcc   - For e.g. gcc-7
+
+2. Environment varibales
+   a. VFC_BACKENDS - For e.g. `VFC_BACKENDS="libinterflop_ieee.so"`