GitHub pull request #3609 of commit d835d5ec9f536e1b4a26c22d2df6192f73601b6f, no merge conflicts.sha1origin/pr/3609/mergeghprbActualCommitd835d5ec9f536e1b4a26c22d2df6192f73601b6fghprbActualCommitAuthorghprbActualCommitAuthorEmailghprbAuthorRepoGitUrlhttps://github.com/JackyYin/bcc.gitghprbTriggerAuthorghprbTriggerAuthorEmailghprbTriggerAuthorLoginyonghong-songghprbTriggerAuthorLoginMention@yonghong-songghprbPullId3609ghprbTargetBranchmasterghprbSourceBranchimprove-install-docGIT_BRANCHimprove-install-docghprbPullAuthorEmailjjyyg1123@gmail.comghprbPullAuthorLoginJackyYinghprbPullAuthorLoginMention@JackyYinghprbPullDescriptionGitHub pull request #3609 of commit d835d5ec9f536e1b4a26c22d2df6192f73601b6f, no merge conflicts.ghprbPullTitleclearer message and hint for libbpfghprbPullLinkhttps://github.com/iovisor/bcc/pull/3609ghprbPullLongDescriptionBcc user should be aware of libbpf when building from source.\r\nI think **libbpf Submodule** is easy to be ignored in the INSTALL.md, so add it into table of contents.\r\nAlso adding a warning message when cmake failed to update git submodule.ghprbCommentBody[buildbot, test this please]ghprbGhRepositoryiovisor/bccghprbCredentialsId6d3daf13-69b8-48b1-9c8f-ec5353264113false<a title="clearer message and hint for libbpf" href="https://github.com/iovisor/bcc/pull/3609">PR #3609</a>: clearer message and hint fo...#114413725587460664bcc-pr #11441144false11449161SUCCESS1631382829867https://buildbot.iovisor.org/jenkins/user/ethercflow/my-views/view/all/job/bcc-pr/1144/git1144https://buildbot.iovisor.org/jenkins/user/ethercflow/my-views/view/all/job/bcc-pr/label=fc25/1144/1144https://buildbot.iovisor.org/jenkins/user/ethercflow/my-views/view/all/job/bcc-pr/label=fc26/1144/1144https://buildbot.iovisor.org/jenkins/user/ethercflow/my-views/view/all/job/bcc-pr/label=fc27/1144/1144https://buildbot.iovisor.org/jenkins/user/ethercflow/my-views/view/all/job/bcc-pr/label=fc28/1144/1144https://buildbot.iovisor.org/jenkins/user/ethercflow/my-views/view/all/job/bcc-pr/label=ubuntu1604/1144/1144https://buildbot.iovisor.org/jenkins/user/ethercflow/my-views/view/all/job/bcc-pr/label=ubuntu1710/1144/1144https://buildbot.iovisor.org/jenkins/user/ethercflow/my-views/view/all/job/bcc-pr/label=ubuntu1804/1144/