[Docs] native-image usage docs updated for --static option

[neomatrix369]

substrateVM: Added some more docs around the --static option, to make it clearer what is and isn't supported by native-image

Built a tested locally using the below commands in the substratevm folder:

${MX} build && ${MX} native-image --help 

--static option when native-image --help was invoked previously read:

    --static              build statically linked executable (requires static libc and zlib)

Currently reads:

    --static              build statically linked executable (at the moment includes static
                          libc and zlib only, hence requires them both. At the moment only
                          supports Linux).

Happy to change it to any other test to convey the same meaning of the message.

This came about post conversations in these issues:

• Support static linking of JNI libs #827 (comment)
• [native-image] [questions] HTTPS support and supplying dependencies like libsunec.so or libsunec.dylib with the binary #1600

[neomatrix369]

@olpaw Any progress with this PR?

[olpaw]

I'd prefer to have the specifics of --static (and it's limitations) to be documented on https://www.graalvm.org/docs/reference-manual/native-image/
cc @olyagpl

[neomatrix369]

I'd prefer to have the specifics of --static (and it's limitations) to be documented on https://www.graalvm.org/docs/reference-manual/native-image/
cc @olyagpl

Is this area available to change via a pull request?

[olyagpl]

@neomatrix369 , website update process is close but not similar.
I'll take care of graalvm.org. Thank you for pointing at missing information!