Fix typos in README_GITFLEXIMOD.rst

[yaochengchen]

Description of changes

Specific notes

Contributors other than yourself, if any:

CTSM Issues Fixed (include github issue #):

Are answers expected to change (and if so in what way)?

Any User Interface Changes (namelist or namelist defaults changes)?

Does this create a need to change or add documentation? Did you do so?

Testing performed, if any:
(List what testing you did to show your changes worked as expected)
(This can be manual testing or running of the different test suites)
(Documentation on system testing is here: https://github.com/ESCOMP/ctsm/wiki/System-Testing-Guide)
(aux_clm on derecho for intel/gnu and izumi for intel/gnu/nag/nvhpc is the standard for tags on master)

NOTE: Be sure to check your coding style against the standard
(https://github.com/ESCOMP/ctsm/wiki/CTSM-coding-guidelines) and review
the list of common problems to watch out for
(https://github.com/ESCOMP/CTSM/wiki/List-of-common-problems).

[samsrabin]

Thanks for this, @yaochengchen. Could you please combine it with your other three typo PRs?

[yaochengchen]

Thanks for this, @yaochengchen. Could you please combine it with your other three typo PRs?

Thanks for review, updated as you required.