fixed typo and unified capitalisation style in Developer-Guide_Build-Options.md

[agatebit]

I fixed a spelling error and some inconsistent capitalisation.
My first PR, be kind :)

[igorpecovnik]

My first PR, be kind :)

Welcome!!

BTW. Build options after this
https://docs.armbian.com/Developer-Guide_Build-Options/#build-options-below-needs-to-be-retested-and-added-above-could-be-deprecated

needs to be tested and if its still works, moved up, under non-deprecated section. In case you want to help more :)

[igorpecovnik]

merge, even its a deprecated section, but if functionality works, its copy pasted. So its a valuable contribution.