Documentation Suggestions for build.rst and lp.pxi

[gtjusila]

Minor documentation suggestion

• Added in "build from source" documentation (build.rst) that DYLD_LIBRARY_PATH should be set on MacOS to ensure that PySCIPOPT can find scip dynamic library during runtime
• Clarified the formatting of entries and entries list for functions addRow, addRows, addCol, and addCols in the LP interface

[Joao-Dionisio]

Thank you @gtjusila! Would you mind updating this line

Please note that some Mac configurations require adding the library installation path to DYLD_LIBRARY_PATH when using a locally installed version of SCIP.

in INSTALL.md, please? Your comment is more informative.

[gtjusila]

Added the note also to install.md and changed all OS X reference to MacOS for consistency.

[Joao-Dionisio]

Thank you!