Created Diagram support (markdown)

Diagram-support.md

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+You can use `flowchart` or `Sequence` as a diagram describing tool.
+
+# flowchart
+![image](https://user-images.githubusercontent.com/11307908/29246519-2d7f2032-8038-11e7-97e3-187d8aad18c4.png)
+
+Please remove back slashes \ before `
+
+```
+\`\`\`flowchart
+st=>start: Start:>http://www.google.com[blank]
+e=>end:>http://www.google.com
+op1=>operation: My Operation
+sub1=>subroutine: My Subroutine
+cond=>condition: Yes
+or No?:>http://www.google.com
+io=>inputoutput: catch something...
+
+st->op1->cond
+cond(yes)->io->e
+cond(no)->sub1(right)->op1
+\`\`\`
+```
+
+# Sequence
+
+![image](https://user-images.githubusercontent.com/11307908/29246524-673697ba-8038-11e7-8d4b-c747a6b9520f.png)
+
+```
+\`\`\`sequence
+Title: Here is a title
+A->B: Normal line
+B-->C: Dashed line
+C->>D: Open arrow
+D-->>A: Dashed open arrow
+\`\`\`
+```
+
+## ref
+https://github.com/BoostIO/Boostnote/issues/771#issuecomment-322023940