ogma-cli: Document cabal update step in README. Refs #100.

[ivanperez-keera]

Modify the installation instructions in README.md to include the cabal update step, as prescribed in the solution proposed for #100.

[ivanperez-keera]

Change Manager: Verified that:

• Solution is implemented:

  • The code proposed compiles passes the tests. Details:
    Docker image:

    FROM ubuntu:trusty
    
    RUN apt-get update
    
    RUN apt-get install --yes software-properties-common
    RUN add-apt-repository ppa:hvr/ghc
    RUN apt-get update
    
    RUN apt-get install --yes ghc-8.6.5 cabal-install-2.4
    RUN apt-get install --yes libz-dev
    
    ENV PATH=/opt/ghc/8.6.5/bin:/opt/cabal/2.4/bin:$PWD/.cabal-sandbox/bin:$PATH
    
    RUN cabal update
    RUN cabal v1-sandbox init
    RUN cabal v1-install alex happy
    RUN apt-get install --yes git
    
    # We install the application first and then test it, in case any tests need to
    # run the tool.
    CMD git clone $REPO && \
        cd $NAME && \
        git checkout $COMMIT && \
        cd .. && \
        cabal v1-install $NAME/$PAT**/ --enable-tests && \
        cabal v1-install $NAME/$PAT**/ --enable-tests --run-tests -j1

    Command:

    $ docker run -e "REPO=https://github.com/ivanperez-keera/ogma" -e "NAME=ogma" -e PAT="ogma-" -e "COMMIT=94a59586aaa46765fccc67d327485940154fa811" -it ogma-test

  • The solution proposed fixes the issues described. Details:
    The issue is with the documentation. We verify the solution proposed by visual inspection.

• Implementation is documented. Details:
  No changes needed.
• Change history is clear.
• Commit messages are clear.
• Changelogs are updated.
• Examples are updated. Details:
  No examples affected.
• Required version bumps are evaluated. Details:
  Bump not needed (change to documentation only).