Doc/gitsubmodules: make some changes to improve readability and syntax
* Only mention porcelain commands in examples
* Split a sentence for better readability
* Add missing apostrophes
* Clearly specify the advantages of using submodules
* Avoid abbreviations
* Use "Git" consistently
* Improve readability of certain lines
* Clarify when a submodule is considered active
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Helped-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Kaartic Sivaraam <kaartic.sivaraam@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>