message: Fix name of cmake build switch in docs.
diff: @@ -26,7 +26,7 @@ Alternatively, on a non-SGX machine, you can build a `virtual` instance of CCF:
  $ cd CCF
  $ mkdir build
  $ cd build
  - $ cmake -GNinja -DTARGET=virtual ..
  + $ cmake -GNinja -DCOMPILE_TARGETS=virtual ..
  $ ninja
  .. note:::
  