kill.md: change signal explanation (closes #616) (#998)
kill.md: change signal explanation (closes #616) (#998)

* add kill signal

* 修改kill相关信号的注释

* kill.md: improve descriptions and formatting

* kill.md: move dashes to outside the tokens

zoisom/tldr,UncommonPleb/tldr,zoisom/tldr,zoisom/tldr,Phizho/tldr,felixonmars/tldr,katekyan/tldr,deekim/tldr,slash3b/tldr,AgamAgarwal/tldr,slash3b/tldr,katekyan/tldr,deekim/tldr,felixonmars/tldr,cptdeka10/tldr,katekyan/tldr,UncommonPleb/tldr,AgamAgarwal/tldr,Phizho/tldr,felixonmars/tldr,UncommonPleb/tldr,cptdeka10/tldr,Phizho/tldr,slash3b/tldr,cptdeka10/tldr,deekim/tldr