cmake: make doc more consistent

cmake/Modules/Packages/USER-MOLFILE.cmake

@@ -1,4 +1,5 @@
-set(MOLFILE_INCLUDE_DIRS "${LAMMPS_LIB_SOURCE_DIR}/molfile" CACHE STRING "Path to VMD molfile plugin headers")
+set(MOLFILE_INCLUDE_DIR "${LAMMPS_LIB_SOURCE_DIR}/molfile" CACHE STRING "Path to VMD molfile plugin headers")
+set(MOLFILE_INCLUDE_DIRS "${MOLFILE_INCLUDE_DIR}")
 add_library(molfile INTERFACE)
 target_include_directories(molfile INTERFACE ${MOLFILE_INCLUDE_DIRS})
 # no need to link with -ldl on windows

doc/src/Build_extras.rst

@@ -73,7 +73,7 @@ If CMake cannot find the library, you can set these variables:
 .. code-block:: bash
 
    -D ZLIB_INCLUDE_DIR=path    # path to zlib.h header file
-   -D ZLIB_LIBRARIES=path      # path to libz.a (.so) file
+   -D ZLIB_LIBRARY=path        # path to libz.a (.so) file
 
 Traditional make
 ^^^^^^^^^^^^^^^^
@@ -1370,11 +1370,11 @@ CMake build
 
 .. code-block:: bash
 
-   -D MOLFILE_INCLUDE_DIRS=path   # (optional) path where VMD molfile plugin headers are installed
+   -D MOLFILE_INCLUDE_DIR=path   # (optional) path where VMD molfile plugin headers are installed
    -D PKG_USER-MOLFILE=yes
 
 Using "-D PKG_USER-MOLFILE=yes" enables the package, and setting
-"-D MOLFILE_INCLUDE DIRS" allows to provide a custom location for
+"-D MOLFILE_INCLUDE DIR" allows to provide a custom location for
 the molfile plugin header files. These should match the ABI of the
 plugin files used, and thus one typically sets them to include
 folder of the local VMD installation in use. LAMMPS ships with a