Update the grammar in the README + add command in build from source process

[jessebot]

• Fixed grammar to sound more natural, some misspelled words, missing words, and some missing commas. (english grammar nerd stuff)

• added yarn --force mentioned in No new versions for MacOS #552 (comment) because otherwise you get:

yarn run v1.22.19
$ yarn build && npx electron-builder
$ run-p build-main build-renderer
/bin/sh: run-p: command not found
error Command failed with exit code 127.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
error Command failed with exit code 127.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

[dubisdev]

Looks great! Thank you @jessebot 🙌