Add Github Housekeeping Section to README.md

Created by: QuickBASIC

This PR updates the README.md file to give best practices for GitHub usage. Many of the site contributors are not familiar with git or GitHub, so I feel it will be helpful to include this information in README file.

This PR also suggests closing all issues that are related to the best practices (close issues that are already fixed, close issues that have been asked to be closed, close issues that were fixed in the site redesign.)

The following Issues are either already fixed by the site redesign, fixed by a pull request by a contributor, or have comments from @rehrar requesting closure:

closes #1 (closed) (site redesign) closes #5 (closed) (site redesign) closes #17 (closed) (fixed in luigi1111/monero-site#1) closes #49 (closed) (vague issue w/ no responses by poster) closes #56 (closed) (fixed in #98) closes #62 (closed) (vague issue w/ no response by poster) closes #101 (closed) (site redesign) closes #109 (closed) (rehrar request closed) closes #142 (closed) (rehar request closed, question answered in issue comments) closes #180 (closed) (fixed in #182) closes #181 (closed) (fixed in #179) closes #195 (closed) (fixed) closes #199 (closed) (rehar request closed) closes #214 (closed) (fixed) closes #225 (closed) (fixed) closes #239 (closed) (fixed in #320) closes #259 (closed) (fixed in #320) closes #221 (closed) (fixed in #286) closes #264 (closed) (fixed in #284) closes #287 (closed) (fixed in #320) closes #289 (closed) (wrong repo / asked to be closed) closes #294 (closed) (fixed by #310) closes #297 (closed) (site redesign) closes #298 (closed) (fixed by #298 (closed)) closes #336 (closed) (fixed by #315) closes #327 (closed) (fixed by #320)