[Docs] Add wiki content to Markdown docs

BUG=none
R=vapier@chromium.org, mseaborn@chromium.org

Review URL: https://codereview.chromium.org/1356253003 .

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](projects_using_lss.md).)
+
+You can compile-test LSS by running:
+
+    gcc -Wall -Wextra -Wstrict-prototypes -c linux_syscall_support.h
+
+## 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`.

docs/projects_using_lss.md

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+# Projects that use linux\_syscall\_support.h
+
+*   Chromium
+*   Breakpad (built as part of Chromium)
+*   Native Client, in nacl\_bootstrap.c (also built as part of Chromium)