docs: update README for supported compilers.
docs: update README for supported compilers.

4Second2None/libbson_tmp,alexeyvo/libbson,Convey-Compliance/libbson,derickr/libbson,4Second2None/libbson_tmp,bjori/libbson,rayyang2000/libbson,mapr/libbson,paulmelnikow/libbson,ajdavis/libbson,ksuarz/libbson,ajdavis/libbson,rayyang2000/libbson,paulmelnikow/libbson,mongodb/libbson,Machyne/libbson,rayyang2000/libbson,mongodbinc-interns/libbson,mapr/libbson,Convey-Compliance/libbson,alexeyvo/libbson,Machyne/libbson,jqk6/libbson,bjori/libbson,ksuarz/libbson,derickr/libbson,4Second2None/libbson_tmp,mongodbinc-interns/libbson,jqk6/libbson,mongodb/libbson,remicollet/libbson,4Second2None/libbson_tmp,Machyne/libbson,rcsanchez97/libbson,paulmelnikow/libbson,remicollet/libbson,Convey-Compliance/libbson,remicollet/libbson,paulmelnikow/libbson,ajdavis/libbson,alexeyvo/libbson,derickr/libbson,rcsanchez97/libbson,ksuarz/libbson,bjori/libbson,paulmelnikow/libbson,Machyne/libbson,jqk6/libbson,mongodbinc-interns/libbson,mongodbinc-interns/libbson,derickr/libbson,rcsanchez97/libbson,mongodb/libbson,mapr/libbson,jqk6/libbson,remicollet/libbson,rayyang2000/libbson