[Docs] Add wiki content to Markdown docs

docs/how_to_contribute.md

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+# How to get an LSS change committed
+
+## Review
+
+You get your change reviewed, you can upload it to
+http://codereview.chromium.org (Rietveld) using `git cl upload` from Chromium's
+`depot-tools`.
+
+## Testing
+
+Unfortunately, LSS has no automated test suite.
+
+You can test LSS by patching it into Chromium, building Chromium, and running
+Chromium's tests. (See ProjectsUsingLSS.)
+
+You can compile-test LSS by running: `gcc -Wall -Wextra -Wstrict-prototypes -c
+linux_syscall_support.h

[vapier, 2015/09/22 16:30:14]

do the _ need escaping ?

[Bons, 2015/09/22 16:35:10]

No, not when it's within a code block.

+`

[vapier, 2015/09/22 16:30:14]

should this be cuddled to the previous line ?

[Bons, 2015/09/22 16:35:10]

Moved it to four-space indent.

+
+## Rolling into Chromium
+
+If you commit a change to LSS, please also commit a Chromium change to update
+`lss_revision` in Chromium's DEPS file.
+
+This ensures that the LSS change gets tested, so that people who commit later
+LSS changes don't run into problems with updating `lss_revision`.