Fix linting errors in description_templates.md

Fix linting errors in https://docs.gitlab.com/ee/user/project/description_templates.html

Related: #284446 (closed)

29:33   error  Avoid using future tense: "will be". Use present tense instead.       gitlab.FutureTense
56:77   error  Avoid using future tense: "you'll need". Use present tense instead.   gitlab.FutureTense
77:6    error  Avoid using future tense: "will enable". Use present tense instead.   gitlab.FutureTense
78:64   error  Avoid using future tense: "will be". Use present tense instead.       gitlab.FutureTense
79:61   error  Avoid using future tense: "will discard". Use present tense instead.  gitlab.FutureTense
95:21   error  Avoid using future tense: "won't show". Use present tense instead.    gitlab.FutureTense
111:69  error  Avoid using future tense: "will be". Use present tense instead.       gitlab.FutureTense
122:54  error  Avoid using future tense: "will only". Use present tense instead.     gitlab.FutureTense

If you'd like to work on this issue, mention @msedlakjakubowski in a comment. Then, in your merge request's description, paste this issue's URL so they become linked.